http://www.aprelium.com/
small stable secure.
not vulnerable to microsoft exploits, will run under a multitude of platforms.
I ran a site getting 500+ megs a day traffic off abyss with an moderately active small forum.
I would advise you to consider it as an alternative to apache and miscrosoft, easier to configure and not vulnerable to some of the more traditional forms of attack.
also there is extensive help in their forums.