I use opaque white acrylic sheets, the thin ones. They stock it at Art Friend in many different sizes and thickness. I got the A3 one that is about 1mm thick, and it cost around $3. A3 is big enough for most small product or macro shots.
I prefer this to the paper, or card I used to use previously, because you can use it over and over again. For card or paper, once you stain it, very hard to use. But for acrylic sheets, you can wipe off.
There are a few problems that you have to be aware of. Firstly, the acrylic tends to spring back when you bend it, so it's quite hard to maintain a nice curve if you're using A3 size, but for bigger sheets of the same thickness, I think it shouldn't be a problem. Secondly, the acrylic scratches quite easily, but I find that those fine scratches usually don't turn up in the photograph. Thirdly, when you just get the acrylic sheet and peel off the protective paper backing, it tends to attract a lot of dust because of static.
Oh yea, don't know if you will find this good or bad, but acrylic sheets are reflective. For me, I like the effect, because I get a nice reflection of the product.
Also, they come in a lot of colors. I bought a black one to use, and it's fantastic. Photo below was taken on the black acrylic, but the curve was not gentle enough, so the reflection curves a lot.
http://photography.byvoid.com/details.php?image_id=145
Hope this helps,
Justin
