Yeah man,
If you want to add lots of muscle mass, heavy weights are the key as well as lots of (healthful) food.
A buddy of mine has packed on a ton of weight (good muscle weight, not beer and donuts weight). He basically does full body type excercises (deadlifts, squats, farmers' walks, snatches heee heee).
The key (along with proper form and stretching) is also to keep a written log of what you do. Instead of 3 sets of 10 or whatever do 5 sets of 5 for each excercise adding weight after each set. You'll be surprised at how much more weight you can lift when doing less reps.
Water water and more water, if your pee isn't clear you're not drinking enough.
My friend actually bought from York Barbell (He's from York) a set of 1/2 lb. and 1lb. plates. With the help of his lift "chronicle" he made sure to add them on each workout. this way, every time he lifted he did more weight (those "little" weights helped him to put on a crap-load of mass and added 50+ lbs. to his bench and other lifts in less than a year)
If you get a chance try to check out a power lifting type 'zine called Milo. Lots of tough "non-pretty" excercised have the best effect (farmers walks, carrying huge rocks..seriously, etc.) just look at a farmer, or watch those "world's Strongest Man" comps on ESPN. That's how most built up their mass.
Another great cheap excercise my teacher actually showed me (he's about 6'3" wasp-waisted type guy, when he was younger he did his pull-ups in 10 sets of 10, adding weights around his waist adding up to 100lbs. on the 5th set) is to get two big USGI-type duffle bags the ones with the zipper on the side. Fill one with about 140lbs. (that's what he used but you can use less) of sand and put that bag into the other, that helps reduce the mess of sand leaking through the zipper. Now lift it above your head. hard as hell due to the shifting weight of teh sand. He deadlifts about 600lbs., and says this is way harder. I believe him.
If you're starting from "very out of shape" start with a lot of calisthenics. Don't forget cardio (running is cheap too) and stretching. the final thing I would recommend is to read as much as you can, and find something you like to do. It sounds silly but it helps.
Later,
R