I am thinking of running a campaign, I have two ideas so far both rather high powered campaigns. 

 The first is Pathfinder where all character will be vampires. The base vampire template is only CR +2 so it is not a major jump though a decent one and if a vampire template with a CR over +2 is used it will cost you levels. I am thinking we will start at level 3 or 4 but is open to change. Pathfinder I am new to but like since it is almost completely open source.
[url=http://www.d20pfsrd.com/home] - Pretty much everything in Pathfinder
[url=http://www.d20pfsrd.com/bestiary/monster-listings/templates/vampire]Base Vampire Template[/url]

The second works as either Pathfinder or 3.5. The basic idea is the same for both and will be familiar to those who have used the Savage Species book. You will pick a monster race, something preferably with a decent CR AND a normal class. All PCs will work with me to develop a levelup scheme so that each level up to your CR you will gain bonuses from your race. A hill giant for example will gain extra STR at a good rate. After you hit your CR you will in effect become an epic version of your previous monster. A demon for example at their CR in levels will have all their normal abilities and each level after will progress as though heading towards becoming a demon lord. This will be rather high powered since you in effect gain 2 levels every level.

The general idea for the world for the monster campaign is something akin to planescape with many interconnected planes being used. Magic will be VERY common due to the nature of the world and high power level of the campaign.