It depends on what your guy likes to do for fun. I personally like going abroad but if I'm staying in the states I would love to do a NBA arena tour when the Spurs go on their rodeo road trip. That would be fun to follow the team to each city for every road game and watch in the arena's. That would be pricey but very fun though.
I've been to alot of places so I would like to go some place or events I've never been that has a solid reputation for being interesting/fun. I would really like to go to Kenya to check out that black rhino preserve and the pink lake. I would also like to attend Carnival or New Years Eve In Rio De Janeiro, Brazil. La tomatina and the Running of the bulls in Spain would be fun to attend also. I wouldn't run with the bulls, I would just watch from afar though.
Places I've been that I recommend depends on what his idea of fun and budget are. Thailand, Hong Kong, Singapore, and Philippines are all pretty fun and not too pricey once you get their. Hong Kong and Singapore prices for lodging and food most likely have went up since the last time I've been. Dominican Republic is also a fun cheap place to relax or party. Costa Rica, Panama and Cartagena, Colombia are fun spots that arent too pricey, on the water but have some really interesting history to soak up