Other options besides K-x for K mount bodies are: K20, K10, istD, K200, and K2000; I think that is all but like others have said any Pentax SLR body will fit.
As for the Ricoh pin, it's easy to remove. I have done the surgery myself on a Sears 135mm Macro and it took maybe 10 minutes. Not sure what that does to the original functionality on a Ricoh body though. It wouldn't be hard to put the pin back in either, but it's not something you'd want to do in the field.
I have had a K-x for a couple of years and like everyone says it's a great camera with really good high iso performance.