How about doing a kitty box? We did a surprise party for my Dad in July who is a massive Beatles fan and always wants to buy (expensive) Beatles memorabilia. He likes his whiskey and being a bloke no one knows what to buy him so every birthday he ends up with about 30 bottles of whiskey! So when we sent out the invitations, we wrote that as some people would like to get Dad a present and don't know what to buy, we'd have a box at the party for them to put in cards and money if they wish. People knew that we weren't outrightly asking them to give money, it was just an option - and everyone thought it was a brilliant idea as it saves them worrying about what to buy. Also, it gives people the option to put it in a card or even just drop the money in on it own if they don't know how much to put in. My boyfriends an artist and made the box out of polyboard with a picture of my Dad on it and my Dad had over �700 at the end of the night. Hope that helps and have a nice wedding! :)