I have a Leitz Prado 6x6 projector with manual feed. It cost about $500 on ebay (5 years ago?) and has a superb, very uniform and bright illumination system together with a very good projection lens. It also runs cool using a halogen bulb (the cooling system is supposedly the same as the one in the Hasselblad projector), though the fan is a bit noisy. I don't use glass cover plates and do need to refocus between the center and edges of the image, though the slides don't "pop" very often (effective cooling system?).

Unfortunately, I use it rarely due to the nuisance of mounting slides and setting the thing up - I tend to look at the transparencies using a light table and loupe. As I get into home developing of E6, I think I will start using it more.