A new favor idea I've seen is to have custom made rubber bracelets. AKA Reminder Bands. These aren't so much my style, but the idea is really cute. I do buy them regularly to support causes, but typically they end up with my nephew to be, and he wears them everywhere. They're popular with the kids these days apparently. I did think they were really cute favor ideas, and I also stumbled upon a site that will make them for you. ReminderBand.com has many different styles and options to choose from, including, but not limited to:
One cute invitation idea I saw online used these bracelets:
Of course, the more you buy, the cheaper they get, and it depends on the style you pick, and any other options you choose.