Bitcointalk user, makomk, has created a utility that scans a hard drive looking for any indications of the missing Bitcoin wallet and the private keys stored within it. Right now this process is somewhat restricted to users who can operate Linux, as you'll need to boot to a live Linux operating system to use the recovery tool.
So, if you've gotten yourself into this precarious situation after formatting your hard drive, to recover your lost Bitcoin wallet, boot to a live Linux distribution and execute the following commands in a command prompt:
- wget http://makomk.com/~aidan/wallet-recover
- chmod +x wallet-recover
- sudo ./wallet_recover
Hopefully, the recovery tool finds its mark(s) and outputs lots of public and private key combinations. If it is successful, it will also generate a file called recovered-wallet.dat, which is a usable Bitcoin wallet containing all of the Bitcoin addresses and private keys the tool could find. It is recommended to take this file, load it onto a USB drive, and open it on another system to check if you recovered your wallet and Bitcoins.
View Bitcoin Wallet Recover source code.
Read the Bitcointalk thread.