which will be the best web server and app server for rails 3
I don't know about the best, but I have decent experiences with NginX & Passenger. I can send you some config files if you would like to take a look at it.
I did try with Thin for app server, but it Passenger does the heavy lifting for you so it's much more pleasant...
Best Regards,
Kresimir Bojcic
You might also try nginx + thin, varnish caching the pages, and perhaps HAProxy for load balancing.