At my place of employment, we are using the Apache package to provide web services. Apache is a full-featured web server with full support for the HTTP 1.1 standard, proxy caching, password authenticated web pages, and many other features. Apache is one of the most popular web servers available (according to a recent site survey done by Netcraft, more than 54% of all web sites on the Internet are using Apache or one of its derivatives), and provides performance equal or better to commercial servers.
( Under construction. :-p )
To keep up with added features and bug-fixes that are made to Apache, it is a probably a good idea to upgrade your server from time to time. The Apache web site is located at http://www.apache.org/ and contains information on the latest versions.