A few minutes ago, I was pleasantly surprised to find out that my latest sponsored post was automatically approved by the system at PayPerPost (PPP). Apparently, if your sponsored posts are consistently approved, they put your blog in auto-approval mode.
This feature, along with their upcoming Argus system that replaces their reliance on Google and Alexa rankings, is keeping PPP at the top of the list for sponsored post services.
Update: This is what Argus looks like right now. Take a gander:



