what are some of his hobbies?
Activities?
Is he into sports?
Does he play games board/video?
What does he do for enjoyment?
What does he like that he doesn't usually have the time for?
Call a party planner if you want this to be really good. Many party stores do stuff like this, though I don't know how much it costs.
Don't know about your budget, but a light lunch/dinner is also nice. While catering can be a little expensive, it is hard to do the food yourself and still keep it a suprise.
www.partygamecentral.com/
www.party411.com/gameguide.html
http://freespace.virgin.net/ken.tew/party/list.html
www.bluepineapple.com/partygames/
party-games.zaural.ru/party-games.html
Hope this helps! Make sure to come back afterwards and let us know how it goes.