I would have to agree with Felt_Rider in that 45 degree leg presses aren't useless as some have claimed. Since I have a bad lower back, I've been able to stimulate the quads very well with 45 degree leg presses. I've actually come to prefer them over squats as I am able to concentrate on quads better and I don't feel the compression on my spine.
One of my favorite leg routines is as follows:
Thigh Extensions: 5 - 8 sets, 12 to as high as 20 reps per set
(I perform these with fairly light weights with little rest between sets so as not to strain the knees and still pre-exhaust the quads)
45 degree leg presses: 5 - 8 sets, 12 to as high as 20 reps per set
Lying Leg Curls: 5 - 8 sets, 12 - 15 reps
Exercises such as hack squats and lunges hurt my knees or I would be doing lunges now.
Keep in mind that I don't train with heavier weights as does Felt_Rider. For one thing, I'm too much of a wuss!
And I have found that my legs respond well to higher reps and a quick pace without going heavy.
Also, keep in mind that I haven't been in good enough condition to handle a routine like this in a few years. If I were to do this today I'd have to be hauled out on a stretcher and the DOMS would be unbearable! Hopefully that will change at some point in the future but right now I'm enjoying the cycling too much to switch emphasis to weight training.