Get down to the local thrift store. Look through the art they have there. It's not likely to be any good, but you might get lucky; in any case, what you're looking for is the frames. In fact, the more horrendous the art, the better, because it's likely to be cheaper!
Get a couple vintage-looking frames and toss the prints of angels and hippie landscapes. If the frames are looking shoddy, spray paint them! A nice glossy black is very chic on a carved frame, or you can just do a touch up with gold paint or a nice stain. What to put inside? We don't recommend you try your own hand at painting--not for your wall. Why not get some cool paper from Papyrus or your local paperie, or frame an interesting piece of fabric?
It's just another easy way to make life more lux for cheap or free.