Macbook Pro won't boot into OSX (circle with line through it), but Windows works fine
I brought it to the Apple store where they replaced the hard disk cable for free (possible thanks to Applecare). OSX works again.  This solution defies logic to me; I didn't think it could possibly be a hardware problem because Windows worked fine.

I am including the relevant parts of their problem writeup below:

Issue: Mac OS partition boots to a prohibitory symbol. 
Windows partition can run fine
Occurred after waking from sleep, computer froze completely 
Steps to Reproduce: Observed at bar 
MRI passes, third party memory 
Booted to 10.8 installer and internal drive did not mount 
Booted to storage diagnostics and no hard drive detected 
Proposed Resolution: Replace hard drive bracket, has third party drive, run storage diags after bracket and see if drive is recognized