I use Gmail, I like the labels instead of folders plus their strong spam filter. Google has introduced some useful extra features in the Labs section under settings.

ReadWriteWeb has a post about Five Fabulous Gmail Gadgets You Won’t Find in Labs. One of them is the Twitter Gadget:

The Twitter Gadget is a recent favorite of ours. Once installed, it provides a box where you can update your status, check your friends’ timeline, read your replies and direct messages, and view your favorites.

I have not tried the Twitter Gadget, I use TweetDeck – Twitter on your desktop.