Do look into nginx + mongrel. I’ve been messing around with it recently and it’s really quite the system, and is the server that many Rails developers are turning to.
A couple of links regarding nginx and Rails
The short: nginx absolutely screams past Apache in benchmarks, is MUCH easier to configure and nearly as feature complete as Apache, with it’s own build in proxy balancing.
Heck, I’ve gotten nginx to proxy back to an Apache process for SVN access in very little time (nginx’s WebDAV plugin isn’t ready for SVN yet, but it’s getting there). Give it a try, it’s quite impressive.