There are a few professional tools that help you find the best potential link partners.
My favorite tool scans the link partners of a competitors site... I review someone with a top ranking and a top pagerank for the industry - enter it into my nifty program - and away it goes.
This tool visits every link pointing to my competitor and reads every page. It records the title, description, and keyword tags, calculates the keyword density on the page, the number of links to that page, and the number of links out from that page - as well as it's pagerank and alexa ranking.
All of the results are exported to excel, where I instantly sort a list of 100's to find the very most valuable links that are pointing to my competitor.
In 20 minutes, I can find a handful actively linking sites with links pages that have a healthy pagerank, lots of links in, few links out - AND that focus exactly on the keyword phrases I'm targeting!
Pure Gold.
Linkbuilder