The next thing you know it'll be a present for the alter boys, priest, chauffeur, waiters, waitresses, hotel manger/cleaners/janitor right down to the barman at the end of the night who won't sell you any more drink.
I hope I'm not too presumptuous but I don't think the majority of fellas would agree with a present for the groomsman, this seems to be more a tradition for the bridesmaids. I'd take the previous posters advice and buy them a few pints.
I havn't heard of groomsmen getting presents, but if you want , maybe a night away and a game of golf or you might find something here www.iwantoneofthose.com
Did you check out the link below? There was a post there about that exact topic recently. Or don't tell me, you posted there aswell lol Weddings Online (WOL)
I actually got my groomsmen new ties which matched the wedding outfit (but were also suitable for wearing to work), thus killing two birds with one stone!