My favorite was Cloudflare because I had a similar idea years ago that I was going to do as a startup, but chose another idea instead.
The tl;dr version of it is a forwarding proxy for your website that speeds up page delivery (gzip, etag etc), filters out vulnerability and exploit attempts, filters out spammers, filters out mis-behaving bots etc.
I am not sure if Cloudflare is application aware. The way that I was going to do it was to build modules for popular web applications and optimize based on that (eg. it would recognize Wordpress and compress the JS/CSS, sideload images, etc.)
Clickable link: https://www.cloudflare.com/
That is an impressive website (even with flash disabled) and a welcome change to the standard screenshot/header/sub-menus/links in footer boilerplate that we see too often.
(As an aside, the winner, Qwiki, is co-founded by Louis Monier - link for those who don't know him or don't recognize the name: http://en.wikipedia.org/wiki/Louis_Monier)
TL;DR: Get going!
Aside from that it seems silly after a while when the make the barrier so low to gaining badges and achievements. Once you start rewarding every little thing it starts becoming less meaningful. It's kind of like getting those Certificate of Participation awards at a science fair. Sure you got an award, but you just had to show up.
Next thing you know badgeville will try to expand into human behavior...creating achievements, points, and badges for every day human things. Stuff like Showering 5 Days in a row badge, Nose Picker badge, and Poop Twice a Day badge... Now that I think about it THAT actually might be more fun.