Has anyone ever made a monogram wedding cake topper from gumpaste or other materials that would be beautiful and not too difficult? Any suggestions would be welcome.

Yep. I make a lot of em'. Rolled curled gumpaste works well! Check mine out. Actually, I think I only have one posted, and I didn't use it as a stand up topper, but it's not any different. You'd just make sure it was dried on a skewer or something to stick it into the cake.