I am not particularly interested in origami as such, but I kind of love Origami Simulator. It’s a very cool use of web technology that’s surprisingly fun to play with!
This is extremely frivolous, but I got a kick out of this browser extension that plays the Wii Shop Channel music on a bunch of e-commerce sites. It makes me feel like I’m spending imaginary points instead of real dollars, which probably has some downside I’m not seeing yet. Plus the Wii Shop Channel music makes for great mashups.