Phylomortis - This neat little site has a bunch of cool scripts, bunches of graphics for earlier versions of RPG Maker (which can be easily converted), and...some stuff. He's also working on an RPG which I insist you must play when he finishes it because he's such an awesome dude.

RPG RPG Revolution - Despite the slightly retarded name, this site has cool forums and resources for RMXP. Go go.