I have to start out by saying that Metacognizant goes a little too far in the scavenging for my personal taste; food out of garbage cans == gross. Generally I restrict myself to furniture and related items of interest, and I would like to share a few thoughts in this area with you, the E2 reader:
There are a few places one can retrieve vast amounts of free furniture. Over the last two years, one of my housemates and I have managed to collect between the two of us (all for free): 1 couch (ugly but comfortable), about 10 (mostly nice) chairs, 5 desks (3 of them very nice), 3 tables (one IKEA-like thing, a glass-topped cocktail table, and an old coffee table), and a plethora of various pieces of rubbish (as examples of this last category, we have an ashtray from a Chicago Boy Scout convention, and around 50 academic journals about French history).
This activity can be done solo or as a group of 2-3.
There are two main sources for this stuff. Number 1: The local college or university. You would not believe how much nice furniture gets thown out by these places. It helps if you are actually attending there, but whatever. I can often wander the halls, looking for stuff that has been left out with a sign reading "Trash", and just pick it up and carry it off. Nobody cares, since it was getting thrown out anyway. In fact, sometimes the maintenance people will simply refuse to take something that's too heavy, and so it will just sit there for months until someone else takes it away. That was the case with a large desk Will (my housemate) and I took from the history department at our school. The damn thing weighed about 200 pounds, and so it sat there in the hall waiting for someone to take it for about 6 months before we decided to disassemble it and move it into our apartment.
You can also often find old computer equipment, some of it pretty decent (17" monitors, old Pentiums and SPARCstations, etc). I got a complete collection of official printed and bound documentation for Unix SVR4 this way too, including some of the 3b2 hardware docs.
Number 2: As Metacognizant mentions, moving households are a great place to get furniture. However, there is another resource, even more vast than people moving. This resource can be tapped when people are evicted from their homes, and their stuff gets thrown out into the street. For whatever reason, this happens a lot in Baltimore. It's kind of sad, but what the hell. Free stuff is good, right? This stuff will go very fast, because everyone can see it sitting there in a big pile. You generally have to get there within an hour or two in order to get anything good.
Alleys are a good place to check too; often garbagemen will refuse to take the big stuff, so you often get a pretty wide window of opportunity for snagging something nice. About a month ago I saw an old arcade game (sans screen) sitting in the alleyway about 100 feet from my house. I considered snatching it up, but I'm moving in about a month, so it'd just be a waste of effort. Still, it was neat, and I'm sure that it wasn't the garbage people who took it - someone driving by saw it and then ran off with it.
As with so many other things (like picking up girls and winning a fist fight), confidence is important. When you grab that piece of furniture, you must know that it is yours to take. That way you don't get questioned about it by maintenance workers or whoever (note that I'm not suggesting stealing here, though I suppose there can be a fine line between scavenging and stealing). Just do the right thing, OK?
Keep in mind that scavenging is not simply a method of saving money. It is, indeed, partially that. But really, I don't need 10 extra chairs (between that and the 3 couches we have, we can easily seat 25 people in our living room - we don't know that many people). So why do I keep bringing them home? Well, hell if I know. But it's fun. Also I figure that if and when I move, I'll be able to sell it all for some cash, which would be cool. But mostly, I find it very relaxing to just wander around the neighborhood, smoking my sticks o' death, and looking for free stuff. I hope you have a good time of it too.
Postscript: I recently moved away from Baltimore (sad!). We sold most of our furniture, all of it way below what we should have/could have sold it for, and scored $225. We spent it on dinners at Martick's and the Black Olive.