404 error pages are usually such a missed opportunity for brand building. Gojee.com made me laugh with this image - such a great way to address what is normally a dry and frustrating experience. Honestly made think better of their brand.
Edit: Twitter’s “Fail Whale” also comes to mind of course… most brands have 404s as a full afterthought. Why… when a simple message here speaks so much about the values of your brand.