50mm lens First of all, make sure you're purchasing a lens that matches their DSLR camera. This lens is a recommendation that I feel very strongly about...here's why.
Tripod If you know someone who likes to take outdoor photos (especially ones where you can see traffic moving at night), they need a tripod. If they don't have one, check out these.
Photo vacation When I travel, I LOVE to take candid photos of other travelers and also night photos in big cities. Depending on what they like, consider travel as a gift! Warning: patience required. :)