My guild uses the zero-sum system. How many other DKP systems are out there? Are there any that are fair for newer raid members, rather than the raid members that have been there the longest, get everything.

There's a whole long thread on this. On the front page.

http://forums.elitistjerks.com/viewtopic.php?id=8835

Do a search for 'Igni' as an author, there's a large thread about this.