For legs, squats are inescapable. And no, no smith machine squats, not half-squats, not leg press, etc. etc. Real squats. Probably the only real variation on squats is box squats, where you start with dead weight from the sitting position.
Once you accept the reality of squats, then lunges, step-ups and even <gasp> leg presses are a great supplement.
P.S. smith machine lunges? For some reason I can only envision that with someone also using that round rubber pad that covers the bar at the same time.