One of the oldest and best ways to increase your search engine rankings and get visitors to your website is from inbound links. The importance of inbound links to your website will most likely never diminish. It's no secret that search engines, especially Google, value quality inbound links to a website for higher rankings. However, these days the emphasis is not on the quantity of links, instead it is on quality. A couple dozen links to your site from related, high quality, authority sites are much more valuable to a search engine than hundreds of low quality links you obtained by exchanging with anyone that would say yes. Read the rest here http://topgptsites.blogspot.com/2007/08/how-to-get-inbound-links-to-your.html
I have to disagree with the 'related' portion of the link. The incoming link that is going to propel your site is going to be a link from a site that has a higher PR than your site has. I have one page that is a PR6 and the ONLY reason it is a PR6 is because it is linked from a PR8. The article that was written on that page was completely off topic of what my site is, but yet there is an obvious corrolation between a very highly ranked page linking to my site and the page having the PR that it does.