I've seen many projectors at the local university's property disposition building over the past couple of years. A couple of months ago I picked up a like-new Kodak Ektagraphic II A projector with a Schneider Vario-Prolux MC 70-120mm f2.8 lens, extra lamps, a 140 carousel and a really nice Kodak black canvas-like case for it all. Cost me $20. The Schneider lens is clearly better than the standard Kodak lens that normally comes with an Ektagraphic. If you live near a decent sized university, chances are you may have the opportunity to get some really cool things, cheap. At the moment, slide projectors are being replaced by digital ones on campus so now is a good time to get a projector.
I prefer the Leica/Leitz/Kindermann/Zeiss projectors with the straight trays but I couldn't pass this unit up.
Any of the generic Sawyers, GAF, or other brands that use a universal 100 slide carousel. Most also can take a straight box magazine as well. I tend to stay away from the Kodak projectors, as they are brand specific for accessories.