Good question. There aren't many. Most of the ones I can think of (Kickstarter, Github, Heroku) launched years ago and have since built on their success without really innovating much beyond the initial idea.

The YC portfolio has a lot of interesting, innovative startups. No products that I use myself at this point, though.

Right now, personally, the new idea I find the most exciting is crowd-funding computer games. Last year I spent a ton of money on Kickstarter to fund small indie developers such as Double Fine.