Mehdoh is a first class Twitter client packed with features and designed to take full advantage of Windows Phone 7.5 (Mango)
Mehdoh can run in the background to let you know when you're mentioned or receive a direct message,, updating the live tile, and popping up a toast notification.
Instapaper and Read It Later support.
Upload images to yfrog, TwitPic, twitvid, or img.ly, or even change your profile photo directly from your phone.
View images, links, and even geo-tagged information from within the app itself. Mehdoh supports a vast array of image hosts (including instagram, twitpic, yfrog, moby pictures, picplz, twitgoo etc... etc...!)
Conversation view lets you view everything that's been said so far with the person you're replying to.
Pin your favourite contacts to the home screen so you never miss a friend's tweet.
Plus all of the usual features you would expect from a modern first class Twitter client, such as @ auto complete, retweet with edit, saved searches, block spammers etc...
Buy it for $0.99 or try it for FREE here