Get big slabs of mdf, glass, wood or laminate? Check the recycling center?
Throw some spare fabric over that puppy and call it fabulous.

Check out the "free" section on your local craigslist. There is often free furniture on there, at least near me. Just don't take anything heavily upholstered if you live anywhere that's experiencing any sort of bedbug resurgence.

The good ol' 2x6 (or 2x8) and cinderblock bookshelf method is great way to get things off the floor, or to get things out of boxes so that you can pack the boxes away.

For table or desk space, you can build a very simple table with 2x4s and plywood, or check out Craigslist for things that're being given away.

I wrote way too much here about wooden storage crates, which we use all over the apartment. I love that they're modular and can be stood upright or set lengthwise, stacked, or fitted together Tetris-style into a larger configuration.

I know it's one more thing to buy, but they cost lots less than proper furniture, and they would fit in your next place, too.

Right now, we're using them as:

- entertainment center. Several 3-cubed cubbies stacked together, the TV on the lengthwise surface of a 3-cube, and a smaller crate snug up against the TV to make the most of the space. Lots of shelving for DVDs.

- a stereo center. Three 3-cubed cubbies stacked horizontally, with the stereo on top. The cubes are perfectly sized to hold smaller 4 CD crates, so you can fill the cubes and still have easy access to the CDS in the back.

- kitchen storage. We use one 4-cube upright in a tiny corner that would otherwise be dead space. It holds cookware, glass bottles and jars full of dry goods, and baskets of onions and potatoes.

In my last apartment, I cobbled together a platform bed from these cubes, laid down eggcrate foam and a mattress, and was perfectly comfortable. When we moved and acquired a proper bed, it was easy to take apart and reuse as bookcases.

I used one 3-cube as a coffeetable for a while, which offered nice storage for oversized books. I think a 2- or 3-cube, nicely finished and with a custom cushion, would make nice extra seating in a window nook or small corner.

You can use those rubbermaid storage totes to hold up planks, creating tables, counters and bookshelves. It's easier than finding cinderblocks. Most of my furniture came either from the Goodwill or off the street. Find out if your town has a specific bulk trash day each month (a lot of them do) and if so, drive around the richer neighborhoods the evening before it. You can find some awesome stuff that way. Haunt the thrift stores. If there's an Ikea near you, stop by regularly to check out that corner where they toss the scratch & dent stuff; it's often marked down 70% or more.

Lumber can be almost as expensive nowadays as just buying some cheap shelving units at Home Depot. I once outfitted an apartment from a used office furniture store.

whenever i move in to a new, bare living space (usually leaving behind my old produce-crate, wire-spool and duck tape furniture), i paint realistic 3-dimensional chairs on all the walls, then i laugh at my friends when they try to sit in them and end up falling on their asses. it's a little trick Wile E. Coyote taught me.