The website is here. I was working on CSS issues with the front page last night when I decided to see how the permalink page looked. To my surprise, I couldn't get to it. I tried a few other post pages -- none were there. Also gone are my category listings and even my 404 page!
I just installed WP last week, but these pages worked as late as this weekend. I didn't make any changes besides CSS stuff since then.
All the files remain on my server, and the permissions are fine. wp-admin works, and I tried creating a new post to see if posts created after the weirdness began would have working post pages. They don't.