check out david halloran for pot calls, think he has some sound files on youtube also or on his website.
i have about 6 or 7 of his calls and they seem to make it in my vest mostly over the last 3-4 yrs. for box calls, most others have mentioned good ones.
Bob harwell on this site makes a great boxcall too.
My favorite pot calls are all made by David Halloran. I've got two, and my dad's got two as well, and both have been very productive for us. I own calls from a few other people, but the Halloran pot calls stay in my vest for every hunt. I've heard great things about Steve Reeves, and would probably look to him if trying another maker for pot calls.
For box calls, the sound varies a bit more, and I prefer to run them myself before I buy. I've got both a long box and short box from Russell Beard that both have a hen trapped inside of them. I've got a Scott's Cutter that sounds great as well, and hope to pick up a Bob Harwell box before spring hits if I can, and plan to get on the list for Mann pretty soon too