from opensecrets.org:Barack Obama (D)
1 University of California $491,868
2 Microsoft Corp $443,748
3 Google Inc $357,382
4 DLA Piper $331,715
5 Harvard University $317,516
Individual contributions $347,909,254
PAC contributions $0
Mitt Romney (R)
1 Goldman Sachs $676,080
2 JPMorgan Chase & Co $520,299
3 Morgan Stanley $513,647
4 Bank of America $510,728
5 Credit Suisse Group $427,560
Individual contributions $192,355,237
PAC contributions $838,481
NOTE: The organizations themselves did not donate, rather the money came from the organizations' PACs, their individual members or employees or owners, and those individuals' immediate families. Organization totals include subsidiaries and affiliates.
edit: to be in compliance with PWA, I'm supposed to say something. Mostly, I just think its important that we know what kind of people are supporting which candidates, because they likely see the candidate as contributing to their company's philosophies in their policies.
An interesting point is that ontheissues puts Obama at strongly supporting topic 16 (stricter laws on campaign financing) and he has no PAC. Romney is almost half PAC and opposes topic 16 overall (though he wanted to abolish PACs in 1994).