I would like to get new a lens for my boyfriend for Christmas. He has a Sony Alpha DSLR-A100. He is an amateur photographer, and bought the camera maybe a year ago. He has no other lenses- just the one that the camera came with. I have no idea where to begin.

Does it have to be a Sony lens? If not, what other lenses are good/work on this type of camera? What kind of lens would you recommend- telephoto?

Any & all suggestions/recommendations would be greatly appreciated.
Thanks.