What kind of portrait lens can be used on Nikon D3000?

I want to buy a single focal length len for Nikon D3000 like 50mm f/1.4 or f/1.8, etc What are the options? Should I buy AF-S or I can use AF as well? Thanks.

Added (1). Thanks heaps. Are there non-Nikon lens that anyone would recommend?

You can use both AF and AF-S lenses. However, only the AF-S lenses will auto focus on your camera.