Free: Contests & Raffles.
Try the search function. This has been discussed many times.It really depends on what you want to do with it and how knowledgeable you are about them or how interested you are to use the functions. Also how much you are willing to spend. I am an advocate of the Garmin GPS 60csx as a good all around work horse.
You can't go wrong with a 60CSx or a 60Cx. The "S" model has a barometric altimeter and magnetic compass. I don't care for them personally, but some do.