Depends on how hard-core an op-shopper you are. Decide on a theme then op shop/disposals your heart out. This can work well if you want to do like a shabby-chique and you're prepared to strip & paint a few bits of furniture, etc. Also, if you have a sewing machine, if you hang around spotlight near the beginning of hte week they often have a lot of stuff on their sales tables (offcuts and suchlike) which you could transmogrify into decoratin splendour. The Ikea catalogues are a good guide to mix-n-matching, often using one or two pieces in a strong colour and then matching your soft-furns to that can work. They also have plain frames you can stretch your own fabric over if you want something matching on the wall.

Our FDC lady has done a few large canvases where she has painted a base colour then attached some wall-stickers to them. Gives the impression of large art without the expense.