The stock fan is adequate for cooling, but it IS noisy, by my standards. I use a Lian Li PC68 and the stock intel CPU cooler is LOUDER than....EVERYTHING ELSE! Only my "cap'n crunch" Maxtor SATA drives can make more noise
The Zalman cnps7000 is the best cooler I've found that provides good cooling AND is quiet. You can barely hear it at the lowest speed, and it's only slightly louder at the highest speed. If you're worried about weight, the Al-Cu version cools pretty much the same I hear.
Nice case btw (the Antec Sonata). I built a PC for school for my brother and I used that case. Very Quiet.