Apache and mod_proxy are an excellen choice if you want to setup a proxy or reverse proxy server.  As an alternative, if you already are running IIS7 or higher, you can configure IIS to proxy requests without the need to install/maintain an Apache instance.

You can even proxy requests to other technology stacks, for example if you are runnign rails or Java, etc., you can proxy requests to webspere and other app servers and have all requests go through the same server/url/IIS instance.

The following link provides an excellent overview of how to configure IIS to proxy requests.

http://www.iis.net/learn/extensions/url-rewrite-module/reverse-proxy-with-url-rewrite-v2-and-application-request-routing