It's a very good question. I always interested in the best links, so if you don't mind I would handle only about them.
Jumpenjuhosaphat wrote a realy useful post about the links in his Internet Marketing Strategies blog with the title
Increasing off page link relevance. Telling the truth it is one of my personal favourite pblog posts, but don't tell him
It describes how to evaluate a link.
Nowadays I start to use google operators in order to collect really powerful links. For instance: allinur:keyword, allintitle:keyword.