ApertureExpert.com is a website helping people learn Apple's photo editing software, Aperture. This is probably the most popular site I've personally worked on, and it's an ongoing project that's been very interesting, with lots of different stuff going on all the time. There's been XML-to-Drupal data migration; ecommerce powered by Ubercart and Amazon Cloudfront; editorial workflows with user-submitted content and scheduled publishing; very active user-to-user forums; cunning use of flags and rules; customization of ckeditor; Foundation, SASS, and Compass-powered frontend development; and more.
As with any site build, there are bits that felt deeply clever, compromises and workarounds for which one might consider feeling shame, and everything in between. We can talk about all of it. If you're a beginning site builder, come in and learn. If you're more advanced, come get shouted down when you try to heckle.