The gym I go to doesn't have any free weight bars to do standard leg exercises like deadlifts or hang/power cleans. All they have are Smith Machines...does anyone know any good leg exercises you can do using dumbbells?
Goblet squats, walking lunges, walking overhead lunges, overhead squats, stiff legged deadlifts, etc 
Tell your gym thayre a fucking joke... demand you some olympic barbells immediately 
Bulgarian split squat
As mentioned above, really only limited by your imagination. DB lunges (all directions) Split Squats, DL variations, Squat variations, etc.
TAKU
After no longer being able to do loaded bilateral standing lifts due to injury, I've found single leg "Bulgarian split squats" with dumbells to be the best substitution for squats. It took a few weeks to get the movement pattern down + perfected, but it feels good now though with comparable stimulation.