Deployment Platform Suggestions?

I'm going to be deploying a rails app in the near future, and am deciding which web server to go with. It seems like all the cool kids are using mongrel, which is not a proper web server, behind some other app. People are also talking about litespeed, and lighttpd was the first server platform for Rails apps I heard about.

Our site gets around 500,000 reqs/day. We're planning on a 2-server cluster behind a hardware load balancer, with a mySQL server and a file server behind the web servers. The plan is to deploy the app code to the two webservers, but serve statics such as images/videos from the file server through a network share on the web servers.

Is there any reason not to use lighttpd in this setup? I've benchmarked both lighttpd and litespeed, and they're both extremely fast, but I haven't delved into setting up Mongrel at all.

I can't wait to deploy this site. The current site running on Apache with a Java backend, besides being ugly as sin, runs at about 1.5 reqs/sec. I've had to restart apache on several occasions when the app(whose author has moved on from the company, thank the lord) has frozen it.

Any suggestions or guidance are welcome.