Monograms are always so fun especially at a wedding. Here are some really cool and cheap letters from Urban Outfitters. The top and below are Acid Etched letters. The aluminum letters ($10/each) are etched with a different pattern but as you can see they're more on the smallish side (approximately 6.5"w, 6" h). The bottom Around the World letters ($12/each) are made out of cardboard and cotton and are slightly bigger (approximately 8"w, 8" h). Both would go really great with any wedding style and after the wedding they would be really cute in the newly wed home!
Obviously, a DIY monogram could easily be made. Craft stores like Michael's and JoAnn sell big cardboard letters that could be dressed up any number of ways however these guys are so cute and cheap that I'd just go and buy these suckers up!