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.

Thanks
Jason