Though this site has been around for a while, I didn't see that anyone had linked to it. learnsanskrit.org
aims to explore how the unique qualities of the Internet can facilitate the task of learning and teaching Sanskrit. To some extent this site is iconoclastic, for although it owes much to both traditional Sanskrit grammar and classical Western philology, it does away with both whenever they make the task of learning Sanskrit needlessly complicated.
The heart of the site is the grammar guide, which has been under slow but steady development for a few years. Featuring thousands of exercises, more than one hundred lessons, and dozens of images and audio clips, the guide presents Sanskrit grammar in a fresh way without sacrificing clarity, depth, or its enthusiastic spirit!