to be honest, i've been pretty impressed with the stock cooling on my 3000+. It's decently quiet, and with it i've been able to OC to 2.55GHz, or 41% above stock. If you got the retail kit (usually only a couple of bucks more than an OEM) then i'd try it out, and if you don't like it, then go buy an aftermarket fan.
If you wanna go aftermarket, i second the Zalman suggestions, i imagine a 7000-AlCu will fit. I've bought several Zalman products and have been extremely satisfied with the quietness and the performance. The AlCu is less than 1 degree warmer, btw, so I'd save $5 and go with it rather than the all-Cu model, esp. considering the weight difference. And the Thermalright XP-90 and XP-120 are nice, too, from what i've heard.