thttpd
Though LightTPD (or “Lighty”) is the darling lightweight webserver of 2005, Jef Poskanzer’s thttpd has been serving static content securely and wickedly fast since 1995 or so.
O’Reilly’s ONLamp.com recently posted a tutorial, “Lightweight Web Serving with thttpd”, which is worth a look if you run a high-traffic site or have underpowered server hardware. The article walks you through installing and configuring thttpd, setting up CGI and virtual host support, and using thttpd as a static content server behind a more full-featured server like Apache.