We love unexpected details and lightswitch covers definitely fall into that category. These have all been made by hand from vintage wallpaper or ephemera and are surprisingly inexpensive:
Sold through Eekowire plates start at $12. We're pretty sure we could make one of these ourselves, but we're not totally sure we'd want to spend the time. Bet we'd be able to get these guys to make one out of a piece of wallpaper we send them (or a vintage magazine).