I LOVE my buckmark. I found mine at a Pawn shop for $200 and added the tac sol barrel mentioned above. Total cost was less than $500.
Another great choice would be a Ruger Mark 2 or 3 especially the 22/45 series (The 22/45 has a grip angle like a 1911, whereas the normal Rugers have more of a glock cant) You will have to send it away to get threaded properly. The Tacsol threaded barrels for the Ruger are serialized parts and you have to transfer through an FFL (The Ruger uses the top half as the serialized receiver.) so it will end up being expensive.
You can also get some good use out of a CZ Kadet for a full sized, combat style pistol.
Don't forget to check out the Advantage Arms .22 conversions for the Glock frames.
My most favorite pistol is my Marvel 1911 in .22lr. It's amazing.
The Ruger will be the most quiet though as it has a small ejection port. I don't know if you could really hear the difference, but shooting it side-by-side with the Buckmark I could tell.
Glockers of the Old Dominion #101