What to do about a "stuck" transaction?
I believe your options are to:


Upgrade to Bitcoin-Qt/bitcoind v0.9 or greater, which takes care of this situation.
Live with it as-is (showing an 0/unconfirmed that will never confirm)
Transfer funds elsewhere and abandon your wallet
Export your keys and import them into another wallet, perhaps a new one
Perform wallet surgery (pywallet to remove the private key used in the double spend, rescan, then import it back in.  Instructions).