biggest I've seen is here on my desk, 62x62 480w @ 15 or 16v (don't recall, i have it written down somewhere) but if found out its impossible to aircool, you *need* water.
however, I've come to realise that even this tec is pretty useless, if you put it on anything "bigger" than a midrange card, the coldside is not gonna be much colder then straight watercooling, for example, my watercooled gpu (hd4870) gets about 40-45 degrees C load temp @ furmark, thats 200w into watercooling. putting the TEC inbetween, you'd need a much bigger, and very good waterblock, to take out almost 700w of heat, and it would get a theoretical 15-20 degree delta between hot and cold, however, I doubt that a waterblock can be made to absorb 700w at the same plate temp as my current waterblock at 200w, and whats the point of having the card run at 20-40 *C over having it run at 40-45 with regular watercooling?
so, adding a pelt to a hd4870 would be useless, and adding it to a slower card, it would be useless in the sense that its useless to slap hundreds of dollars to a cheapo card to make it run somewhat faster, while you can get a much faster card for much less then the total spent..
so... get a phase change unit for the same amount it would cost to pelt and watercool something, it works much better