dinde, Dangerden makes some excellent quality waterblocks; I'm using 2 maze1c waterblocks on one of my dual AMD rigs. The suggestion that Soldat made about checking out watercooling at overclockers.com is a good one; they have many experienced watercooling people at those forums. Also, to do watercooling right and to minimize chances of leaks pretty much precludes using cheap components. Be sure to use a premium water pump such as an Eheim and go with either silicone or Tygon tubing because it lasts much longer and can tolerate sharper bends without collapsing like vinyl tubing will. You can go with the modded heater core that DD sells instead of the high priced radiators though as it will cool a dual rig with no problems. Another place that sells watercooling stuff and are premium people to deal with is
Dtek Customs. The radiator I'm using is the one at Dtek listed as the "core combo", which also has a nice fan shroud for a 120mm fan for $48. It's basically the same heater core that DD has, but has the shroud which improves cooling efficiency. I'm using a Panaflo 120 X 38mm M1A fan on the radiator.
A peltier element is a Thermoelectric Device that moves heat from one side of itself to the other electrically. You are talking pretty big money to be using a TEC and watercooling; you have to have a separate psu just for the peltier element and you will be dealing with some serious heat production that will be exhausting in your room. I've also been down that road and you can get some remarkable overclocks out of your processor but it is almost as expensive to do the watercooling/TEC route as it is to get a Vapochill case. PM me if you wants some specifics on costs on setting up a watercooling/TEC setup.