Not a huge fan of all-in-one watercooling, but they are relatively compact.
If you are going to get one I would suggest the Corsair H100, but if you aren't going to overclock the CPU then the stock cooler will be "ok" (not great), or check out a good air cooler (Thermalright Archon or similar).
If you are planning to overclock or prefer watercooling then I would suggest the
XSPC Rasa 750 RS240. For approximately the same cost of the Corsair H100 but MUCH better performance, with the added virtues of being able to be added to or modified in future. It's a little more involved than the H100...but not by much.
The other all-in-one solutions (Corsair H50/H60/H70/H80, Antec Kuhler H2O 620 and 920) don't offer a significant performance upgrade over a good air cooler, and have the added disadvantage of being fairly loud when the fan(s) are run at high r.p.m. If a single radiator all-in-one is what you are looking for then the
H80 is probably the best of the bunch...although the price doesn't thrill me.
I would suggest you make sure about RAM compatibility before shopping for aftermarket coolers. A system will POST with the stock Intel cooler...there's a chance it won't with the wrong memory.