What's a good lens focal length for taking pictures of small products?

I'd like to get a prime lens for my DSLR to take pictures of small products -- say, other cameras -- for selling online and such. My question is, what's a good single focal length to get for this purpose? Normal, like 50mm? Short telephoto, like an 85mm? How about macro lenses, like a 50mm macro or 60mm macro? Since I have a DSLR with a 1.5x focal length field of view multiplier, I understand that a 50mm lens basically becomes a 75mm field of view, an 85mm lens becomes a 128mm field of view, etc. Thanks a lot!