Robin Good: Ethan Lyon at YouMoz has put together a great simple tool inside a Gdoc spreadsheet (public, free and open) that allows you to automatically find sites and blogs where you can make guest posts.
Guest posts on other quality and thematically-relevant sites is an effective strategy to build quality incoming links to your site.
I have tried out this litte great gem and I must say: it does work. You simply input the keyword representing the topic you want to write guest posts for, and the spreadsheet automatically kicks out URLs that you can go and check out right away.
This great tool scans Twitter to find messages that offer opportunities for guest posts and lists them for you.
Go try it out now:
http://ow.ly/8x9gF (make sure to make a copy first)