It's always nice if a gift could be a surprise, but he needs to go with you to help pick out the one he wants. Proper fit is very important for cycling. If makes riding much more enjoyable and less prone to injuries.
Take him down to your local bike shop (or visit several different shops and decide on which one you feel more comfortable with). They will have a selection of road bikes, hybrids, cruisers, etc.
All the major brands mentioned in the previous posts are of comparable quality, it's mostly a matter of preference.