LOL the problem with buying links is that the money and effort would be better used on building content for your site so people want to link to it.
Natural backlinks, and the fastest way to get backlinks is to get a story on Digg's frontpage. Anyways, if you want I can get you a PR5 in the next update, PM if interested.
Getting good back links is the way to go. I have had success building back links by using free press releases. If its written well, you could get picked up by some heavy hitters