One more thought on heatsinks ... I really like the heatsinks for XEON processors, like this one on ebay. Xeon heatsinks typically have a nice flat "bottom", ready to bolt leds onto.
clickyThe one in the link is huge, but that's not bad if you have the room. Increases in the price of copper and aluminum I think have a lot of cheap heatsinks getting melted down, which is a bummer :(
I like screws (4-40 hex-cap stainless) instead of epoxy, but both work fine. Using thermal epoxy (Arctic Silver for example), less is more. You want only a grain of rice or two sized bead of epoxy in the center of the LED module, and then use a clamp or vice to put a lot of pressure between the module and the heatsink, squeezing that epoxy into a very thin layer.
See this video for the basics:
Youtube
