If you’re new to renting links, text-link-ads has a comprehensive white paper on the subject.  If you’re not new to renting links but you haven’t read the paper, it has some good link building tips.

Though TLA will tell you anything to get you to buy their product, the paper is, for the most part, right on.  It actually mentions other methods of building inbound links.  One thing that is inaccurate in the paper, however, is how long you should wait to see results.  The paper says you should wait at least 90 days… that may be the case for Yahoo or MSN, but for Google, it’s a good six months or longer for competitive terms.