The Twitter web page is nice, but it lacks the functionality of a stand-alone application. For several months I’ve been using Twhirl, by Seesmic. Twhirl is good, but now there’s something much better, Seesmic Desktop.
With Seesmic Desktop I can have columns for both Facebook and (multiple) Twitter accounts. I can add photos to tweets and shorten URLs. I can like and reply and direct and share. One of the nicest features is the ability to create userlists to organize “friends” based on the nature of the relationships. It’s brilliant!
Seesmic Desktop runs on the Adobe Air platform, which is very nice (and easy).