I just downloaded Witty after seeing several of my twitter friends mention it. I had all but given up on Twitter tools as they all usually stink (several are based on the Adobe Runtime [AIR], maybe that's a coincidence, maybe not). This one appears to actually WORK which is a big criteria for me using software (I know, I'm a romantic). It also looks damned sexy too! Check it out:
If you want it, check out its home page.