The biggest bet I've heard of and been given proof is the 7000 BTC gamble on Justdice. The second highest one I've seen was one by QS on primedice, profiting him 150 BTC 
As I understand it, PrimeDice has a maximum payout of 20 BTC (or is it 40 BTC?) but that includes your original stake, too. So there's no way to profit 150 BTC.
The 7000 BTC bet by mechs was the 27th in a series of 27 bets he made in a few days, all over 1000 BTC. He won the first 26 of them:
Quote
1 2013-10-02 07:34:43 #148575723: 1767.51587669 BTC @ 92% hi: lucky:19.0776 profit: 134.48490980 bal:1902.00078649
2 2013-10-02 07:34:53 #148575921: 1767.51587669 BTC @ 92% hi: lucky:12.2165 profit: 134.48490980 bal:2036.48569629
3 2013-10-02 07:35:39 #148576957: 1767.51587669 BTC @ 92% hi: lucky:73.9495 profit: 134.48490980 bal:2170.97060609
4 2013-10-02 07:42:12 #148584193: 2170.97057849 BTC @ 92% hi: lucky:60.4122 profit: 165.18255156 bal:2336.15313005
5 2013-10-02 07:43:30 #148585325: 2336.15313005 BTC @ 92% hi: lucky:79.5807 profit: 177.75078975 bal:2513.90391980
6 2013-10-02 07:48:30 #148590355: 2513.90372740 BTC @ 92% hi: lucky:52.1169 profit: 191.27529235 bal:2705.17901975
7 2013-10-02 07:49:13 #148590882: 2513.90372740 BTC @ 92% hi: lucky:93.7250 profit: 191.27529235 bal:2896.45431210
8 2013-10-02 07:51:02 #148591949: 2896.45431590 BTC @ 92% hi: lucky:57.2928 profit: 220.38240367 bal:3116.83671957
9 2013-10-02 08:01:57 #148601047: 3116.83674877 BTC @ 93% hi: lucky:92.4414 profit: 201.08624487 bal:3317.92299364
10 2013-10-02 08:12:54 #148612542: 3317.92314519 BTC @ 93% hi: lucky:82.9679 profit: 214.05956096 bal:3531.98270615
11 2013-10-02 08:19:29 #148618898: 3533.97982021 BTC @ 95% hi: lucky:45.0747 profit: 148.79913916 bal:3682.77895937
12 2013-10-02 08:21:04 #148620446: 3682.77897204 BTC @ 95% hi: lucky:56.5205 profit: 155.06436614 bal:3837.84333818
13 2013-10-03 22:16:36 #151396071: 3846.94273818 BTC @ 93.01% hi: lucky:41.2406 profit: 247.74957520 bal:4094.69231338
14 2013-10-03 22:16:56 #151396629: 3846.94273818 BTC @ 93.03% hi: lucky:90.6891 profit: 246.86927929 bal:4341.56159267
15 2013-10-03 22:17:12 #151397027: 3846.94273818 BTC @ 93.09% hi: lucky:78.7297 profit: 244.23066127 bal:4585.79225394
16 2013-10-03 22:17:36 #151397665: 3846.94273818 BTC @ 93.2% hi: lucky:33.1190 profit: 239.40201721 bal:4825.19427115
17 2013-10-03 22:21:15 #151403104: 4825.19427115 BTC @ 94.3% hi: lucky:40.0573 profit: 240.49216990 bal:5065.68644105
18 2013-10-03 22:24:13 #151406494: 5065.68648587 BTC @ 94.55% hi: lucky:17.7951 profit: 238.41673708 bal:5304.10322295
19 2013-10-03 22:27:04 #151408897: 5304.10330755 BTC @ 95.09% hi: lucky:05.4491 profit: 218.09910565 bal:5522.20241320
20 2013-10-04 05:01:01 #151911402: 5519.94840009 BTC @ 95.21% hi: lucky:97.9878 profit: 219.73115077 bal:5739.67955086
21 2013-10-04 05:01:05 #151911481: 5519.94840009 BTC @ 95.21% hi: lucky:59.0951 profit: 219.73115077 bal:5959.41070163
22 2013-10-04 05:02:56 #151914007: 5959.41068558 BTC @ 95.51% hi: lucky:26.6702 profit: 217.76091885 bal:6177.17160443
23 2013-10-04 05:04:58 #151915792: 6177.17161758 BTC @ 95.71% hi: lucky:47.1520 profit: 212.33823588 bal:6389.50985346
24 2013-10-04 05:08:04 #151919268: 6389.50987008 BTC @ 95.81% hi: lucky:98.4443 profit: 212.73911449 bal:6602.24898457
25 2013-10-04 05:11:39 #151923159: 6602.24886053 BTC @ 95.95% hi: lucky:34.1439 profit: 209.86825940 bal:6812.11711993
26 2013-10-04 05:14:24 #151926184: 6812.11702310 BTC @ 96.04% hi: lucky:09.6031 profit: 209.95278458 bal:7022.06980768
27 2013-10-04 07:22:09 #152097271: 7016.28891331 BTC @ 96.2% hi: lucky:03.5475 profit:-7016.28891331 bal: 0.00000000