I'd like a simple, efficient, scalable HTTP server written in C ...
Check out libebb - http://tinyclouds.org/libebb/. It was created by Ryah Dahl (node.js fame) and is a solid piece of software. We used it in our WebROaR server for ruby web applications.
Sidenote: libebb's Ragel based parser is derived from Mongrel.
Sidenote: libebb's Ragel based parser is derived from Mongrel.