It's totally a marketing project, but the team at Sugru have machined a pretty sweet multi-chamber water pistol. Its use of the actual Sugru product is clever--this Instructables guide shows how the team utilized the putty to connect and seal PVC pipes for the pistons and insulate the electronic switches. Maybe a little superfluous when building an overly complex water gun, but a cool project nonetheless. I've used Sugru in the past for more practical applications, like repairing frayed laptop power cables (an alternative to electrical tape) and making recessed buttons on smartphones more prominent/proud. It's also very compatible with LEGO bricks.