since you have a quadcore and a 8800, i'd recommend a thermochill PA120.2, if you have the money to spare for it though, its more than double the GT Stealth, but you'll get much better performance
Tygon is the best quality tubing you can get, but it is more $$$ like thermochill, so its budget here....clearflex is a great second choice
I would get a swiftech mcw60 for the 8800GTS (i think it works on the 2900 too) - it has low restriction, good cooling, and a fair price. Full body blocks from dangerden and EK are often overrated and have higher restriction + higher $$$. The memory chips shouldn't get too hot, but if you have room, get a fan to blow across the copper ramsinks
As for the water vs. air, there are great HSF's out there (ultra 120, ninja, etc) but air cooling for your setup probably might be louder than a watercooling setup - it really just depends on what budget you're willing to spend. A quick estimate summary: pump ($80), CPU block ($60), GPU block + sinks ($80), tubing ($10-15), reservoir ($20), additives ($5), rad ($50-120) any accesories: clamps, fittings, etc.. ($5-10)...compared to a air-setup, cpu heatsink, gpu heatsink, fans
If you decide air cooling, i would get a Scythe Ninja + yate loon D12SL-12, yate loon case fans, Thermalright HR-03 for the 8800GTS + 92mm fan (silverstone FN91, akasa amber, nexus, arctic cooling are all decent)...
i would stick to air-cooling, since you can cool the 3.3 ghz Q6600 w/ a good CPU cooler, and the 8800 w/ the HR-03, all thats left is good case flow for the HDs...maybe 2-3 yate loons on a fan controller, then you're set
and by the way, YOU HAVE A PS3??!! how is it, since i was thinking about getting one later in the year...