I have to confess to being a great fan of twitter clients. In fact for me it was the turning point - from a irregular to a regular user of Twitter.
You can also set it up for multiple accounts. I gave this a try, thinking this would be a good way of keeping tabs on both my personal and work account - however after finding I had tweeted something I had meant for my personal account on the work one - my advice is make sure you know how it works before experimenting!! (thankfully it was library related).
I've used Bit.ly a lot in the past, but again Twitter now shortens URLs automatically, so I use it less. In the future I may try Twittermail - I can see it could have potential, but don't have a need for it just now.