The Thermaltake Frio and Dark Rock have both been well received. Water's not really necessary for the 2600K IME.
Sorry to link to Bit-tech..
http://www.bit-tech.net/hardware/coo...ooler-review/3
http://www.bit-tech.net/hardware/coo...ock-advanced/3
I'm under water and at 4.7ghz/1.38v 24/7 folding and I felt the difference in my room temp in coming from a 1366 i7 970 system - they kick out so much LESS heat that it's quite noticable. Core temps are about 51C, whereas on an i7 rig with the same loops I was at 80C.
I'd also consider the H60/70 systems from Corsair as they are so cheap for a basic water cooling rig