Well, cantenna's are great, but keep in mind, you have to send AND recieve a signal, so it'd be like shouting through a bullhorn accross a football field and expecting to hear someone whispering back from the other end...
There are some ways to get a better signal; but sme of the best would be your neighbors upgrading their antenna's from the stock "duck" antenna's that come with their router...
Though, I'd suspect you're not exactly legal in your ISP acquization, so I doubt you'll be able to do that lol...