Your wallet.dat file is what contains your private keys, the other files are just the blockchain, chainstate, debug log, and peer information and are automatically redownloaded/recreated if they are missing. Just copy your wallet.dat into Bitcoin-qt's datadir before you run it, and your bitcoins will reappear once the blockchain is downloaded (though don't delete your backup, you may need it again). If you've already reinstalled Bitcoin-qt, just replace the wallet it generates for you when it isn't running, and save a backup of the new wallet and/or import the keys from it if you used it for anything in the meantime.
PSA on backups: Bitcoin-qt sends change to different addresses that are stored in the wallet.dat file unless you set a specific change address (which is potentially less secure, though not significantly). It generates 100 to start with, then creates more as necessary; however, the new addresses won't be in your backups, so periodic backups are necessary to ensure that you don't lose anything in the event of a crash or if your computer is lost or stolen. This is done transparently, meaning you won't see the other addresses unless you specifically go looking for them (and there's no particular reason to unless you're curious), but it's something to keep in mind so you don't forget to back things up every once in a while.
Great description of what to do should my computer get hosed. Thanks for such a short, clean version.
