i agree with scott. Reeds classic palming dvd is really a nice resource. One other technique you can use (that i got from david stones coin magic vol. 1) depending on the context of the routine is drop one coin on another as you make the classic palm to cover the sound (or really do anything to cover the sound. but i wouldn't suggest just coughing really loud like you were trying to cover a fart). Also david williamson has as click pass (i don't remember if its his or if he credited someone) on "sleight of dave" where he pretends to throw one coin into his left hand to join another but really slaps it into right hand classic palm (where there is a coin already palmed) and uses the sound that creates as the sound for the left hand... if that makes sense.
These kind of techniques all depend on the context of the routine though. And you can't necessarily jazz them in. They have to be built into the routine.
actually in this video i do the stone technique at 50 seconds and the williamson technique at 55 seconds if you want to actually see them.
http://www.youtube.com/watch?v=TKTp8zo26xY
But the point is, anything you can do to hide or justify the sound that slapping one coin onto another while classic palming makes will do the trick. BUT, if you can work on soft palming then you won't really need to hide the sound because there doesn't have to be any. So go take a look at reed's dvd if you really want a good classic palm.