I bought a kit that came with whatever blue coolant, works just fine.  Watercooling a 5870 and 5830 with it with a dual 120mm radiator, keeps them about 40 or so, depending on my ambient heat.  I used 1/2" OD 3/8" ID primoflex tubing with the regular fittings, no compression.

I used a kill coil.  Way less fuss than having to worry about oil or drops of whatever.  Just stick it in the reservoir and call it a day.