Because you like the NDP or flaky independent or because you don't like either the Conservative or Liberal options?
I don't particularly like any of the candidates in my riding. Last election, the Liberals won my riding by about 10,000 votes. So they parachuted in a guy that they hope will be high profile in the future. But, I am not sure it will do much good - he may lose to the Conservative candidate (same guy as last time) based on my completely unscientific lawn sign observations. I might just hold my nose, spin around three times and jab my finger at the ballot.