Someone suggested this on my blog (or maybe it was on here!). Here's what I'm looking for.
1. Roll customizable dice, at least of the form: Xd20 +/- Yd6
2. Total those rolls if possible.
3. Be able to be authenticated. Like the Ref gives you a code corresponding to your roll and you make it?
4. Be deliverable via text or Tweet.
Ideally, in online/text RP, the Ref would call for a check: Make an attack roll (XXX - where XXX is the code for the roll). The player initiates the program, it rolls the appropriate dice, and a text is sent to the player (and ref?) with the result.