Go Karting may be fun if there is one near you, or a day out at a local race track be it horse or grey hound, you could put people into teams, have them place team bets and pay a small prize to the winning team? Or you could organise a murder mystery night or a casino night, you can hire the tables for about �200 per table which come complete with croupier.
Another day out which may be fun is to do the maze at Longleat, you could organise a day in the safari park and then end up at the maze (if it still exists) when I did it, it took us a couple of hours to work out how to get round to the middle. Once again you could put people into teams and offer a prize to the winners.
Hope this has helped a bit, there are lots of web sites offering corporate days out if you need any more ideas. My company is doing Go Ape by the way at the end of March, we are all looking forward to it!