My 2 cents:
There's no reason to overdo it on legs. I'm not saying you shouldn't work them at all, but leg development for most people isn't a problem.
Personally, I would limit it to squats (if you even DO them... I don't think they're necessary) and some bodyweight stuff. IMO, it's far more effective for overall leg strength and balance, but it won't make your legs blow up like balloons, either.
Here's one of my favorite leg day routines:
Warm-up for at least 10 minutes on the elliptical, treadmill or bike. Get a light sweat going to make sure the blood is flowing well before attempting the squat.
Squats:
All of these are ass to ground. I don't do parallel squats. IMO, full squats are better, because they keep your ROM high, and allow you to fully develop your hips. Hips are key in maintaining good balance. Also, I just put in some arbitrary numbers. I don't know how much you squat, but keep in mind that going all the way down is (at first, it's significantly more so) more difficult than doing a parallel/half-squat.
Here's a pretty good discussion on full-squats vs. parallel.
http://www.alwyncosgrove.com/leg-training-myths.html
Warm-up, bar only, 15 reps
Bar + 45s, 12 reps
Bar + 25s/45s, 8 reps
Bar + 35s/45s, 6 reps
Bar + 45s/45s, 5 reps
Make sure you put your butt on your heels for these. Can't stress that enough. Doing that will work your entire leg, hamstrings included. And whatever you do, don't use a Smith machine. Use a squat rack. Smith machines limit your movement too much and force you to move in an unnatural way.
After that, just do a leg-finisher.
Leg Matrix:
This should be performed with no rest in between the movements, all bodyweight stuff
24 single-leg squats (12 per side, again, butt to heels if you can... if not, use a 25 lbs plate held out straight in front of you for extra balance as you go down)
24 Bulgarian Split-squats (12 per side, non-alternating)
24 Alternating lunges (12 per side, alternating)
24 Jump lunges (12 per side, alternating)
24 Squat Thrusts / bodyweight squat jumps
Rest 2-3 minutes, do 2-3 sets
(If you can't do the first two movements, which are difficult, you can just do 24 bodyweight squats instead)
Shouldn't take you more than half an hour to do all of this, which leaves 25 minutes for HIIT. I wouldn't even do this more than once a week. IMO, it's not necessary.
Just as an aside, I don't even do conventional squats any longer, except where I incorporate them with my circuit training (and even then, I'm only doing ATG reps of 135). I just do the leg matrix.
And just to throw even more confusion into the squat thing, check out this vid.
http://www.functionalstrengthcoach3.com/squats.html
I'd like to say that I disagree with the guy, but I can't. I mean, the guy knows his shit. He's coached athletes in the NFL, NBA, MLB, NHL, MLS, Olympics, NCAA, and more.
Hope this helps.