Twicca for Android
I've been a long time Twidroid user, ever since I tried out a G1, ages ago. I even spent the paltry US$3.99 to get the pro version. Blow for blow, Twidroid still has the best featureset, but it ain't the prettiest app out there. I've been hearing talk of Twicca for a while now, and finally decided to give it a shot. So I uninstalled Twidroid, and I've been using Twicca as my primary Twitter client for the past few days.
I absolutely love it. It's lightweight, pretty (just look at that widget!), has a clean and intuitive UI, and a rich featureset - which can be expanded with plug-ins. Best of all, it's free.
There are one or two niggles, but it's mostly language-related, and it's understandable, as the dev's native tongue isn't English.
I'm not too sure I'll go back to Twidroid any time soon.