Benjamin linkAlong with a Williams peep sight
Link here to make it complete and you'll be set.
The Benjamins aren't exactly quiet at full power but they are effective and they move very little when you shoot so they're easy to shoot accurately.
Both of mine are 177. a 22 is a little slower but it thumps bunnies a little harder.
Let us know what you choose!
P.S. the older 5mm /.20cal work fine too but there are not many pellets to choose from for .20 cal. Just a FYI...