DSiPaint

DSiPaint is probably the most popular DSi/3DS site out there. It has many features, including Blogs, Forums (Bulletin Boards), Polls, Chatrooms, an in-development RPG called The Mystical Journey and more.

Orgination
DSiPaint was created by HullBreach, also known as Danny or Daniel. The first members include SavantInamorata (HullBreach's wife) and Skunkman.