I started out with a D80 and Sigma 30mm f/1.4 lens. Tis a great combo, an old school efefctive 50mm prime.
I think it taught me a lot about composition early on. (though it's still early for me) The lack of zoom meant I wasn't afraid to move my feet if needed, crouch down, lie in the mud etc. Now I've got my first zoom lens I find that the zoom simply adds to my movement and does not replace it.
If you're happy to go prime then anything around the 25-35mm raqnge would end up aorund 50mm effective due to crop factor.