Even lighting is extremely important when it comes to product photography. A few small shadows are not a big deal, but you want to display your item in such a way that nothing is hidden. If you have an external flash, use it! For the best results you may want to make a soft box, which will eliminate shadows, and create a soft light that will better display your product. Of course there are some larger items that will not fit in a soft box, but anything smaller, like CD's, MP3 players and small electronics are best photographed that way.
As for actual camera settings, I tend to shoot at F8-F11 for maximum sharpness and depth of field. I use matrix/zone metering, iTTL flash (not balanced fill flash) and ISO200-400. ISO 400 works well because it gathers just enough natural light to minimize shadows, while not introducing noise into the image.
If you still have the products original box, try to fit that in the photo as well, it helps reassure the buyer it is not a fake. In my experience an item with the original box is more likely to attract buyers, and sell for a higher price. Don't be afraid to experiment with different styles either. I have only taken product photos for eBay items, so nothing too serious, but I figured most people who might read this would be selling on eBay or Craigslist anyway.