The first thing is to start searching for a better gym. Why pay monthly fees for that? A gym that has a smith machine but no rack...SUCKS. I'm being totally serious.
If other gyms are too far away but you have room at home then save up and get your own equipment and you'll end up with a better gym than that...which will pay for itself quickly compared to gym fees.
There are plenty of things you can do with dumbells. And also, if you can clean it, you can do front squats with a barbell. Single leg stuff as mentioned above like split squats, lunges, step-ups, Pistols.
There are also goblet squats and you can use dumbells for front loaded squats in the clean position.
Overhead squats. The list goes on and on.
If your back is hurting use another row besides pendlays. Maybe one-arm dumbell rows, for instance.
You could try front squats and split-squats for your 5x5.
I have to agree with Kane that a leg press is probably somewhat a better choice than a smith. Since I think an open chain movement is probably better than a closed chain with a fixed motion. But normally closed-chain would be better. You don't need to settle for leg press, though.