Man I have a ton of info in this. I did a lot of testing and prototyping a while back. I had a water cooled setup that I ran that I could bring a 2 lb chunk of aluminum down to 5F in about 20 minutes. I used 6 70W modules and it drew 36 amps but it showed what it would do.
I also built one that was made into a full sized cooler but it drew 30 amps as well. Used it camping hooked up to my Wifes car with a battery charger. It did pretty well but they take a while to cool down fully. You need a really large heatsink on the "hot" side and one about 1/3 the size on the cold side. Use fans on both. The biggest thing is the Delta temp (the temp between both sides). Most will pull around a Delta T of about 70 deg temp differential, so the cooler you keep the hot side the cooler the cold side gets. The reason most of the off the shelf ones suck so bad is that the fan on the hot side isn't moving enough air.
If you go to
http://www.mpja.com/products.asp?dept=60
These guys have a pretty good selection and you can even get a setup with both heatsinke already attached. If you go it alone use the largest heatsink you can get away with on the hot side and a fan over 100 cfm for a small project. Keep in mind a setup like like this will draw 6 -7 amps all day long. In order to use a thermostat you will need some serious insulation on the cold side, or it will never turn off. Another thing is that when it turns off the heat on the hot side will travel back to the cold side (heat moves from hot to cold, always and forever). I'll dig up a few other pics when I get a chance.
Jeff
Edit: There is a cheap controller kit I'll have to look that up as well