No, seriously, WordPress
1) Because you already know it.
2) Just about every cheap hosting plan in the galaxy offers a one-click installation of WordPress.
3) WP will shield you from the underlying OS, so you won't need a degree in computer science. Or to deal with Linux, for that matter.
I think this site demonstrates that WordPress can be more than just a blog. People who get into the guts of it usually have this epiphany that "hey! this isn't a blog, it's a Content Management System" and you realize you can build any kind of Web site with it that you want.
And without dealing with Linux.