Got an invitation to a fundraising event I wouldn't normally attend (though great cause). This year, a card was inserted with a picture of earrings that had been donated - and on reverse said $10/ticket for raffle - and made it easy to include credit card info. As I reached for my wallet, I realized it's a really good fundraising idea. Why not give everyone a chance/reason to participate easily, even if not attending?
Although I'd include options of fax and online donations on the card too instead of just ability to mail back the card.