This link was sent to me by e-mail, a blog posting called "50 Awesome Tools for Researching Your Family History." This post was on the "Bootstrapper" blog, which apparently specializes in lists: mostly business tips and the like.
Many of the site mentioned on the page are your standard links such as Ancestry.com and the Library of Congress. However, there are a few sites that I hadn't ever heard of such as Geni.com and GenCircles. It's worth a look.