Another option would be to build an external cooling system. I could have a small case (~6" cube) containing a reservoir, radiator, fan and pump (both powered by an integral psu). I could then run a couple of water tubes into the case via a spare pci slot. There are many advantages that I can see to this approach, including:
1) Minimal impact on my PC case, and easy to move between cases
2) I can position the cooling unit for best cooling and least noise
3) The reservoir can be filled easily
4) I don't have to buy a special reservoir, I could use any water-tight vessel
The only difficult issue I foresee is finding a nice enclosure for the cooling unit. Might be an interesting project. Something like
THIS perhaps?