You could install WordPress on Nginx. There are a number of resources to help:

• nginx Compatibility plugin

• HOWTO: Install WordPress On Nginx-

• Slicehost discussion

• How To Speed Up WordPress With Nginx And WP Super Cache

• WordPress on nginx + lighttpd + FastCGI + php

• Nginx as a front-end proxy cache for WordPress

Some performance information from that last link (which appears to be a bit different setup than the others):

So I decided to put a proxy in front of wordpress to static cache as much as possible. ALLn-authenticated traffic is served directly from the nginx file cache, taking some requests (such as RSS feed generation) from 6 pages/second to 7000+ pages/second. Oof. Nginx also handles logging and gzipping, leaving the heavier backend apaches to do what they do best: serve dynamic wordpress pages only when needed.

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On nginx – it’s so efficient it’s scary. I’ve never seen it use more than 10 to 15 meg of RAM and a blip of CPU, even under our heaviest load. Our ganglia graphs don’t lie: we halved our memory requirements, doubled our outgoing network throughput and completely leveled out our load. We have had basically problems since we set this up.