I had a product called Gutter-Loov installed a couple years ago, and it's working very well. It goes under your first course of shingles, and fits under the outer lip of 'standard' guttering. Cost me $7.50 per foot, installed (in 2005). So far, no clogs, and no leaves, twigs, 'helicopters' from the maples, or acorns from the oaks that are all around the house. I'm pretty happy with that!.
My neighbor liked the looks of mine so much that he had it installed on his house, too. Kinda funny, the first really hard rain we had after I'd had it installed, I looked out to see the neighbor standing in my yard, closely watching my roof to see how well the Gutter-Loov was working. He didn't really believe it'd work. Musta made him happy, though, since he got it, too.