I keep sticking Will-o'-the-wisp into all sorts of decks, with varying amounts of success. It worked really well when Eater/Keyhole decks were everywhere because I could stick it on R&D and wait to fire it until I could actually afford it --- when the runner isn't using Eater, you have to use it the first time they make a successful run on that server because the low trash cost means they get rid of it immediately. Given that it costs 4 to rez, I've had to let runners trash them because I couldn't afford 4 credits after I had rezzed ICE on the server.
Which brings me to the latest combo-wombo jank I've been tweaking: Breaker Bay Grid with Will-o'-the-Wisp. Living the dream is a server with The Root, rezzed with Breaker Bay Grid and protected by Will-o'-the-Wisp to rez everything else on the board for cheap.