I'm new to Twitter and I was looking for a simple but effective Twitter client. I somewhat not prefer to use the Web interface.
I searched and found a few simple clients like Bluebird and Canary but they didn't comply to the new Twitter authentication standards introduced in August. So, you couldn't log-in with them and use them. No idea why their new versions are taking so much of time.
So, I was stuck with Tweetie which I was thinking to avoid considering it servers you advertisements. But after downloading and using it I realized that it is very very good.

Doesn't server you adverts the way you might be thinking. It doesn't bother you at all.
There are a few Adobe Air based Twitter clients like Tweetdeck, but then I also wanted to avoid them.
So, here's how Tweetie looks:
You can view a person's timeline:
Also view his bigger profile picture if he has uploaded one:
Also view the tweets directed @ or mentioning somebody:
And Profile information obviously:
It supports a good array of URL Shortening and Image Services:
You can mark tweets as your favourites and it supports multiple accounts.
The only down point I see is no Growl integration and no Retweet button.