Not on Twitter yet? Then you’re missing out on the most popular microblogging site today — as well as the cool new green initiatives twitterers are coming up with! Here’s the latest in the green twittersphere:

>> Start an energy efficiency competition via Twitter. Green-minded geeks are tweaking the Kill-A-Watt Electricity Usage Monitor, a gadget that shows you how energy-efficient your electric devices are, to create the Tweet-A-Watt. This twitterfied device electronically tweets a person’s daily energy use, posting it for all to see and hopefully, spurring eco-friendly competition among Twitter friends.

>> Raise money for charity on Twitter. Who knew microblogging could spur so much micro-donating! BlogHer details some past fundraising successes using Twitter — and reports on the upcoming Twestival on Feb. 12, which “will combine an online twitter fund raising with local offline events.” Create your own Twitter account so you don’t miss out on the Twestivities.

>> Get eco-motivated by fellow green twitterers. At CNet, Elsa Wenzel put together a list of green tweet feeds, from CNet’s own green tech tweets to The Oil Drum’s peak oil tweets. Oh — and my own Twitter feed’s mentioned too!

Happy tweeting!