Are you doing a real site, or a spam site?
Most logical for users while still decent for search engines is probably something like...
http://www.example.com/digital-camer...ybershot-1234/
Depends on how many levels you have etc.
My own way of doing things is...
www.example.com/products/345/name-of-product/
I find having the product ID in the URL makes it much easier to maintain, even if the URLs look a bit uglier. Keeps the URL to a reasonable length too, adding categories in there can get out of hand if you don't keep the names short.
But if you going for rankings hard-core, probably better ways of doing it.