It's a two-party system. If you vote for a liberal non-democrat it is EXACTLY the same as voting for George Bush. If you vote for a conservative non-republican it is EXACTLY the same as voting for John Kerry. The type of electoral system your country uses should inform your vote.
This depends, though, on where you live. I live in Utah, so I'll be voting for Marilyn Chambers (for Vice President - I don't remember the name of her running mate). I wouldn't throw away my vote if there was any chance in hell that it could count, though. If you live in a remotely competitive state, though, voting for a 3rd party is just cutting off your nose to spite your face.