There is a thread around here or in the archives called something like "best practices: dkp" (I didn't find it in a few searches -- if not a "best practice" thread it was started by the same author that starts most of those). Very long and most of it talks about the advantages and disadvantages of various systems.
Buried in there in that huge thread is some info on DKP mods.
Here is what I recall other than EQDKP and nDKP, both of which the consensus is that they are not so great:
EPGP --
http://code.google.com/p/epgp/wiki/WhatIsEPGP_v1
WebDKP -- my guild just started using this, its ok.
I'm sure there are more (well, there is suicide kings but that isn't so good for larger raids and can be gamed).
I like the principle of EPGP myself, and all modifications to it would be easy --- its purely a mod so its just editing some LUA.