a few thoughts. there are numerous types of peltiers (sealed, non-sealed, different amp ratings, different recovery, efficiency, etc). it's more than just getting one of the commonly used 40x40mm chips. as far as the clamps go, copper is good for the cold side as it conducts the cold better. aluminum is good for the hot side as it dissapates heat well. the hardest part to get right is the clamp itself. i took a trinity motor cooler and chopped one in half (2 dremel grinding blades later). it works well, but... given the hastle, cost, and fact that i now have one that works better, i probably wouldn't bother doing it again.
i got mine from p and c racing (http://www.pandcracing.com)
. beyond the fact i can frost my motor can/endbell, they got the clamp part 'right'. i do find that removing motor stickers also makes a noticeable difference.