The PCMechanic guys take four open-source RSS readers & do a feature comparison to see which should take up some space on your desktop. They don't cover any of the readers for browsers, such as Sage for Firefox, or IE's native abilities.

"Some new browsers have this feature, but a dedicated application is still the best way to organize and easily work with feeds from dozens of sources. And due to RSS popularity, there are dozens of readers available on the Web."