I went with something like this :
http://skyrimcalculator.com/#56025
Although I started with a Bosmer because poison resist is awesome and I enjoy sniping people. With this build you focus on basically being completely unseen and killing the enemy before they can even see you. Which is crazy fun. Alternatively, you could go with (I'm gonna catch a lot of flak for this...) Altmer. Let's be honest, Sneak is one of the easiest skills to level, especially with the High Hrothgar exploit. Why Altmer? Base magicka for Illusion spells. Completely different build, but you can sit back and watch your enemies tear each other apart and then pick off the lone survivor with an arrow or a smash with a dagger. Or if you're lucky you get an awesome assassination animation, which is always a plus. Just a thought.