Thanks for the bukkit recommendation - it really is a great minecraft framework to code against. I've since added a ScriptCraft bukkit plug-in...
https://github.com/walterhiggins/ScriptCraft/blob/master/buk...
I used to be very active on the team there, but haven't contributed any code for a while now. I get the urge almost every week, so maybe I should jump back in for a bit.
It has its problems, but is miles ahead from where we started and really does enable plugin authors in a way straight modding never can.