I have the Antec 300 case, with the top fan set on medium.
On a related note, sometimes it seems like one of the fans starts and stops. It sounds like it might be the Intel stock fan, but I'm not sure. Is this normal?
Those temperatures look good to me for the stock HSF. As far as the fan starting and stopping the CPU fan shouldn't be stopping at all check it out visually to see if its operating. Although I'm sure you would be seeing higher temps than that if it was stopping so I'm going to assume it's another fan.