Digsby
A very useful (if slightly bloated) application that links social networking sites (Facebook, Myspace, Twitter and others), IM clients (AIM, MSN, and others), and E-Mail clients (Yahoo, G-Mail, Hotmail, and others). It is nice to have everything in just one program, without having to open 4 different programs and 6 different browser tabs just to get caught up with the morning news. RSS feed integration is in the works, and I can't wait.
Best of all, it's free.