I know this sounds like I'm snubbing you, but in truth, Yahoo site explorer is the best thing I know of to find places to backlink.
Code:
http://siteexplorer.search.yahoo.com
For example, I've been innundated with blog comments since SerpScraper came out. I take the spammer's URL from the comment and look up his backlinks on Yahoo site explorer and see where he's been getting comments or profile links to stick.
If you find a good page to leave backlinks on, don't stop there, look at all the other comments and see who else left a keyword backlink and research those sites for backlinks as well. You will find some really good sites for backlinks if you invest the time.
I've managed to pick up some PR 4 - 6 backlinks this way.
As an added bonus you get some good keyword ideas and they did all the keyword research for you!
Another option is to use Angela's backlink packs with a twist. Read his thread to see how to find your own places to backlink.
Code:
http://www.blackhatworld.com/blackhat-seo/black-hat-seo/87734-how-find-all-angela-edwardss-high-page-ranking-backlinks-free.html
Keep track of your profile backlinks rss feeds and submit them to RSS aggregators to get your profiles indexed. (Not my idea but a good tactic to get your backlinks indexed.)
Then set up a Google Alert for "angelae8654" to email you when Google finds a new instance of that word - usually it is going to be a new property that Angela has placed her backlink and you can too. (This is not my idea and I take no credit. I read about it here last night, but can't find the thread.)
There are many other threads on BHW that can teach you how to do forum, profile, blog commenting, bookmarking, and Web 2.0 site backlinks to your site. A little searching and an butt load of reading is all it takes.