What else can you check on a 1996 Cavalier if you have replaced bulbs fuses and switch but still do not have any low beam headlights?

It probably is the dimmer switch. Dimmer Switch has been replaced already....same effect. The ground wire for the low beams is probably corroded--it happened to me twice! Remove the cowl covering the headlights by removing the plastic rivet tabs--use needle-nose pliers and pull stragght up on the small inner discs. With the cowl removed, you'll see the headlight wires runing in front of the radiator between the headlights. They may be secured to a body arm by a zip strip or two. Cut the strips and pull the wire assembly up so you can get a good look at it. All the wires will be wrapped in electrical tape. Before peeling the tape, look for evidence of corrosion, like a small patch of grainy greenish-blue stuff. If you find it, you've found the corroded part. Peel the electrical tape off, cut out the corroded section, bridge the gap with a new piece of wire and, optimally, solder it together and use shrink sleeves to cover the connections. Remember to slide the shrink sleeves on before you solder the second connection. Re-wrap with electrical tape, and re-secure to the body arms with zip strips.