Members at WebmasterWorld who have been diligently watching Google datacenter changes have compiled a list of datacenter IP addresses. There are far more known IPs than ever before (519 of them within 39 separate Class C's, if I counted correctly), and there are likely quite a few that are still unknown. You can see the list at WMW (msg #26) and contribute to the list if you know of some that are missing. At the time of this writing, here are the known Google datacenter IP addresses (which may not be live at all times).
1. 64.233.161.18
2. 64.233.161.19
3. 64.233.161.44
4. 64.233.161.80
5. 64.233.161.81
6. 64.233.161.83
7. 64.233.161.84
8. 64.233.161.91
9. 64.233.161.93
10. 64.233.161.95
11. 64.233.161.98
12. 64.233.161.99
13. 64.233.161.99
14. 64.233.161.100
15. 64.233.161.101
16. 64.233.161.102
17. 64.233.161.104
18. 64.233.161.105
19. 64.233.161.107
20. 64.233.161.115
21. 64.233.161.133
22. 64.233.161.147
23. 64.233.161.184
24. 64.233.163.19
25. 64.233.163.44
26. 64.233.163.80
27. 64.233.163.83
28. 64.233.163.84
29. 64.233.163.99
30. 64.233.163.100
31. 64.233.163.101
32. 64.233.163.104
33. 64.233.163.107
34. 64.233.163.115
35. 64.233.163.133
36. 64.233.163.184
37. 64.233.163.189
38. 64.233.167.18
39. 64.233.167.19
40. 64.233.167.44
41. 64.233.167.80
42. 64.233.167.81
43. 64.233.167.83
44. 64.233.167.84
45. 64.233.167.91
46. 64.233.167.93
47. 64.233.167.99
48. 64.233.167.104
49. 64.233.167.107
50. 64.233.167.115
51. 64.233.167.133
52. 64.233.167.147
53. 64.233.167.184
54. 64.233.169.19
55. 64.233.169.44
56. 64.233.169.80
57. 64.233.169.81
58. 64.233.169.83
59. 64.233.169.84
60. 64.233.169.99
61. 64.233.169.104
62. 64.233.169.107
63. 64.233.169.115
64. 64.233.169.133
65. 64.233.169.184
66. 64.233.171.18
67. 64.233.171.19
68. 64.233.171.44
69. 64.233.171.80
70. 64.233.171.81
71. 64.233.171.83
72. 64.233.171.84
73. 64.233.171.99
74. 64.233.171.100
75. 64.233.171.101
76. 64.233.171.102
77. 64.233.171.103
78. 64.233.171.104
79. 64.233.171.105
80. 64.233.171.107
81. 64.233.171.115
82. 64.233.171.133
83. 64.233.171.147
84. 64.233.171.184
85. 64.233.179.19
86. 64.233.179.44
87. 64.233.179.80
88. 64.233.179.81
89. 64.233.179.83
90. 64.233.179.84
91. 64.233.179.91
92. 64.233.179.93
93. 64.233.179.99
94. 64.233.179.100
95. 64.233.179.101
96. 64.233.179.104
97. 64.233.179.106
98. 64.233.179.107
99. 64.233.179.115
100. 64.233.179.133
101. 64.233.179.184
102. 64.233.183.17
103. 64.233.183.18
104. 64.233.183.19
105. 64.233.183.44
106. 64.233.183.80
107. 64.233.183.81
108. 64.233.183.83
109. 64.233.183.84
110. 64.233.183.91
111. 64.233.183.93
112. 64.233.183.99
113. 64.233.183.103
114. 64.233.183.104
115. 64.233.183.107
116. 64.233.183.115
117. 64.233.183.133
118. 64.233.183.147
119. 64.233.183.184
120. 64.233.185.19
121. 64.233.185.44
122. 64.233.185.80
123. 64.233.185.81
124. 64.233.185.83
125. 64.233.185.84
126. 64.233.185.99
127. 64.233.185.100
128. 64.233.185.101
129. 64.233.185.104
130. 64.233.185.107
131. 64.233.185.115
132. 64.233.185.133
133. 64.233.185.147
134. 64.233.185.184
135. 64.233.185.189
136. 64.233.187.19
137. 64.233.187.44
138. 64.233.187.80
139. 64.233.187.81
140. 64.233.187.83
141. 64.233.187.84
142. 64.233.187.91
143. 64.233.187.93
144. 64.233.187.99
145. 64.233.187.104
146. 64.233.187.106
147. 64.233.187.107
148. 64.233.187.115
149. 64.233.187.133
150. 64.233.187.184
151. 64.233.189.44
152. 64.233.189.80
153. 64.233.189.81
154. 64.233.189.83
155. 64.233.189.84
156. 64.233.189.104
157. 64.233.189.107
158. 64.233.189.115
159. 64.233.189.133
160. 64.233.189.184
161. 66.102.1.44
162. 66.102.1.80
163. 66.102.1.81
164. 66.102.1.83
165. 66.102.1.84
166. 66.102.1.91
167. 66.102.1.93
168. 66.102.1.104
169. 66.102.1.107
170. 66.102.1.115
171. 66.102.1.133
172. 66.102.1.184
173. 66.102.7.18
174. 66.102.7.19
175. 66.102.7.44
176. 66.102.7.80
177. 66.102.7.81
178. 66.102.7.83
179. 66.102.7.84
180. 66.102.7.98
181. 66.102.7.99
182. 66.102.7.100
183. 66.102.7.101
184. 66.102.7.102
185. 66.102.7.104
186. 66.102.7.105
187. 66.102.7.106
188. 66.102.7.107
189. 66.102.7.115
190. 66.102.7.133
191. 66.102.7.147
192. 66.102.7.184
193. 66.102.9.18
194. 66.102.9.80
195. 66.102.9.81
196. 66.102.9.83
197. 66.102.9.84
198. 66.102.9.99
199. 66.102.9.100
200. 66.102.9.101
201. 66.102.9.102
202. 66.102.9.104
203. 66.102.9.107
204. 66.102.9.115
205. 66.102.9.133
206. 66.102.9.147
207. 66.102.9.184
208. 66.102.11.99
209. 66.102.11.100
210. 66.102.11.101
211. 66.102.11.104
212. 66.102.11.106
213. 66.102.11.107
214. 66.249.81.18
215. 66.249.81.19
216. 66.249.81.44
217. 66.249.81.80
218. 66.249.81.81
219. 66.249.81.83
220. 66.249.81.84
221. 66.249.81.99
222. 66.249.81.100
223. 66.249.81.101
224. 66.249.81.102
225. 66.249.81.104
226. 66.249.81.107
227. 66.249.81.115
228. 66.249.81.133
229. 66.249.81.147
230. 66.249.81.184
231. 66.249.83.19
232. 66.249.83.44
233. 66.249.83.80
234. 66.249.83.81
235. 66.249.83.83
236. 66.249.83.84
237. 66.249.83.99
238. 66.249.83.100
239. 66.249.83.101
240. 66.249.83.104
241. 66.249.83.107
242. 66.249.83.115
243. 66.249.83.133
244. 66.249.83.184
245. 66.249.83.214
246. 66.249.85.19
247. 66.249.85.44
248. 66.249.85.80
249. 66.249.85.81
250. 66.249.85.83
251. 66.249.85.84
252. 66.249.85.99
253. 66.249.85.104
254. 66.249.85.107
255. 66.249.85.115
256. 66.249.85.133
257. 66.249.85.184
258. 66.249.87.99
259. 66.249.87.104
260. 66.249.87.106
261. 66.249.87.107
262. 66.249.89.19
263. 66.249.89.44
264. 66.249.89.80
265. 66.249.89.81
266. 66.249.89.83
267. 66.249.89.84
268. 66.249.89.99
269. 66.249.89.104
270. 66.249.89.107
271. 66.249.89.115
272. 66.249.89.133
273. 66.249.89.184
274. 66.249.91.18
275. 66.249.91.19
276. 66.249.91.44
277. 66.249.91.80
278. 66.249.91.81
279. 66.249.91.83
280. 66.249.91.84
281. 66.249.91.91
282. 66.249.91.93
283. 66.249.91.99
284. 66.249.91.104
285. 66.249.91.107
286. 66.249.91.115
287. 66.249.91.133
288. 66.249.91.147
289. 66.249.91.184
290. 66.249.93.19
291. 66.249.93.44
292. 66.249.93.80
293. 66.249.93.81
294. 66.249.93.83
295. 66.249.93.84
296. 66.249.93.91
297. 66.249.93.93
298. 66.249.93.99
299. 66.249.93.100
300. 66.249.93.101
301. 66.249.93.104
302. 66.249.93.106
303. 66.249.93.107
304. 66.249.93.115
305. 66.249.93.133
306. 66.249.93.184
307. 72.14.203.99
308. 72.14.203.100
309. 72.14.203.101
310. 72.14.203.102
311. 72.14.203.104
312. 72.14.203.107
313. 72.14.203.133
314. 72.14.203.147
315. 72.14.203.184
316. 72.14.205.99
317. 72.14.205.100
318. 72.14.205.101
319. 72.14.205.102
320. 72.14.205.104
321. 72.14.205.107
322. 72.14.205.133
323. 72.14.205.147
324. 72.14.205.189
325. 72.14.207.99
326. 72.14.207.100
327. 72.14.207.101
328. 72.14.207.102
329. 72.14.207.104
330. 72.14.207.106
331. 72.14.207.107
332. 72.14.207.133
333. 72.14.207.147
334. 72.14.207.184
335. 72.14.209.99
336. 72.14.209.101
337. 72.14.209.102
338. 72.14.209.104
339. 72.14.209.107
340. 72.14.209.147
341. 72.14.211.99
342. 72.14.211.100
343. 72.14.211.101
344. 72.14.211.102
345. 72.14.211.104
346. 72.14.211.107
347. 72.14.211.147
348. 72.14.211.184
349. 72.14.215.19
350. 72.14.215.44
351. 72.14.215.80
352. 72.14.215.81
353. 72.14.215.83
354. 72.14.215.84
355. 72.14.215.99
356. 72.14.215.101
357. 72.14.215.102
358. 72.14.215.104
359. 72.14.215.107
360. 72.14.215.115
361. 72.14.215.133
362. 72.14.215.147
363. 72.14.215.184
364. 72.14.217.99
365. 72.14.217.101
366. 72.14.217.102
367. 72.14.217.104
368. 72.14.217.107
369. 72.14.217.147
370. 72.14.219.99
371. 72.14.219.100
372. 72.14.219.101
373. 72.14.219.102
374. 72.14.219.104
375. 72.14.219.107
376. 72.14.219.147
377. 72.14.221.99
378. 72.14.221.101
379. 72.14.221.102
380. 72.14.221.104
381. 72.14.221.107
382. 72.14.221.147
383. 72.14.223.99
384. 72.14.223.100
385. 72.14.223.101
386. 72.14.223.102
387. 72.14.223.104
388. 72.14.223.107
389. 72.14.223.147
390. 72.14.235.99
391. 72.14.235.100
392. 72.14.235.101
393. 72.14.235.102
394. 72.14.235.104
395. 72.14.235.107
396. 72.14.235.147
397. 72.14.253.99
398. 72.14.253.100
399. 72.14.253.101
400. 72.14.253.102
401. 72.14.253.104
402. 72.14.253.107
403. 72.14.253.147
404. 216.239.37.19
405. 216.239.37.44
406. 216.239.37.80
407. 216.239.37.83
408. 216.239.37.84
409. 216.239.37.91
410. 216.239.37.98
411. 216.239.37.99
412. 216.239.37.101
413. 216.239.37.104
414. 216.239.37.105
415. 216.239.37.106
416. 216.239.37.107
417. 216.239.37.115
418. 216.239.37.147
419. 216.239.37.184
420. 216.239.39.19
421. 216.239.39.44
422. 216.239.39.80
423. 216.239.39.81
424. 216.239.39.98
425. 216.239.39.99
426. 216.239.39.101
427. 216.239.39.104
428. 216.239.39.105
429. 216.239.39.106
430. 216.239.39.107
431. 216.239.39.115
432. 216.239.39.133
433. 216.239.39.184
434. 216.239.51.19
435. 216.239.51.44
436. 216.239.51.80
437. 216.239.51.81
438. 216.239.51.83
439. 216.239.51.84
440. 216.239.51.99
441. 216.239.51.104
442. 216.239.51.107
443. 216.239.51.115
444. 216.239.51.184
445. 216.239.53.19
446. 216.239.53.44
447. 216.239.53.80
448. 216.239.53.81
449. 216.239.53.83
450. 216.239.53.84
451. 216.239.53.98
452. 216.239.53.99
453. 216.239.53.101
454. 216.239.53.102
455. 216.239.53.104
456. 216.239.53.105
457. 216.239.53.106
458. 216.239.53.107
459. 216.239.53.115
460. 216.239.53.133
461. 216.239.53.147
462. 216.239.53.184
463. 216.239.57.17
464. 216.239.57.18
465. 216.239.57.19
466. 216.239.57.44
467. 216.239.57.80
468. 216.239.57.81
469. 216.239.57.83
470. 216.239.57.84
471. 216.239.57.98
472. 216.239.57.99
473. 216.239.57.103
474. 216.239.57.104
475. 216.239.57.105
476. 216.239.57.106
477. 216.239.57.107
478. 216.239.57.115
479. 216.239.57.133
480. 216.239.57.147
481. 216.239.57.184
482. 216.239.59.17
483. 216.239.59.18
484. 216.239.59.19
485. 216.239.59.44
486. 216.239.59.80
487. 216.239.59.81
488. 216.239.59.83
489. 216.239.59.84
490. 216.239.59.91
491. 216.239.59.93
492. 216.239.59.98
493. 216.239.59.99
494. 216.239.59.101
495. 216.239.59.102
496. 216.239.59.103
497. 216.239.59.104
498. 216.239.59.105
499. 216.239.59.106
500. 216.239.59.107
501. 216.239.59.115
502. 216.239.59.133
503. 216.239.59.147
504. 216.239.59.184
505. 216.239.63.19
506. 216.239.63.44
507. 216.239.63.80
508. 216.239.63.83
509. 216.239.63.84
510. 216.239.63.91
511. 216.239.63.93
512. 216.239.63.99
513. 216.239.63.101
514. 216.239.63.104
515. 216.239.63.107
516. 216.239.63.115
517. 216.239.63.133
518. 216.239.63.184
519. 216.239.63.189