This was last night's quad workout. I'm a firm believer in higher reps on legs. Otherwise you develop size and no separation. I won't post weights as that is not important and everybody is different. I do squats on a smith machine so I can adjust my stance to isolate quads better. Here goes.
Warmup with a few light sets of squats, leg presses, and leg extensions.
Pick a weight you can do 20-25 time on squats and do 20 reps
Striaght to the leg press, another 20 reps, you should almost need help to finish the set. Straight to the leg extension machine. Pick a weight you can only do 10 times, drop the weight and do another 10, drop and do your final 10.
Stumble to the bathroom and puke. Wash the taste out of your mouth and go back for more. Repeat the series 3 more times with no rest between exercises and only a 2 minute break between cycles.
I use many different quad workouts and am always changing, but this is one of the best.