Depends on the day, and who's running them. Also a lot of our stuff is BJJ specific... I'll run you through how I generally warm-up the class when asked:
Start but jogging around the mat. Durring the jog we shuffle to the inside of the circle, then outside, run backwards, jog bringing knees up high, bringing our heels up to our butts, crisscross/crossovers/grapevine (we call them any of these names) both inside and out. Sometimes we'll assum low wrestling stances, still circling, and sprawl on the leaders command. Sometimes we'll walk shortways, and sprint the lengths of the mat. Sometimes while jogging the circle on command we'll stop quickly touching both palms to the mat then leaping as high as we can. This portion varries quite a bit depending on who is running our warm-up. I know when I do it I do all of the first exercises, and usually pick one of the last three. I don't count laps really, but typicly do these circle jogging until I'm slightly out of breath (usually the last exercise does a good job of this) and am beginning to feel a sweat.
After this we do varrious mat warm-ups by making three lines and doing at least one mat length of the following. Shrimp crawls, shrimp then stepping through to belly, reverse shrimp, butt scoot forward and backward, pull ourselves across the mat on our bellies using only our arms, alligator crawl, inch-worm, straight forward rolls (not shoulder), rear rolls over shoulder, cartwheels (one length facing one way, one length the other), and Judo (shoulder) rolls left side, then right.
That is usually where I turn it over to my instructor. Other exercise options people use (not necissarily in addition to the previous) are: run with partner in a firemans carry to on end of the mat, do 10 squats and run back and alternate. Using a belt behind the back and under a partners armpits drag them up and back on the mat (kind of like rows). Guard sit-ups with a partner (have partner in guard and sit-up at angle so your armpit end over their shoulder). Leg-ups with partner throwing them down to sides. Jumping guard with partner. Jump guard on standing partner, take their back (without touching the floor) and continue round to front, then change directions.
Anyway, you get the idea. It sounds like a lot, but really normally it isn't more than the set I explain I typically use. Some days it's harder though.