My apartment has NO good light, so this is a problem for me too. I shoot mine on white posterboard, then run them through FotoFuze. I used to shoot them on white fabric, but posterboard is easier.
FotoFuze is kind of annoying: the brush is round, so it's hard to make straight lines and right angles. However, it's the best free product I've found so I stick with it. It took me a while to get the hang of it, and at first the white background looked REALLY weird. If you stick with it and play with it, it works but be prepared to spend a lot of time editing!
After I FotoFuze them, I go back to Picasa (a free photo editing software from google) and adjust the lighting. Since the lighting in my house is so bad, I usually use the "fill light" and "highlight" settings a lot.
Then, I reupload them to Etsy!