While finding the EyeTV link for my last post, I discovered that El Gato has, in my opinion, the best take on a 404 page (the one that comes up when you request an invalid URL). Sure, generally everyone has a "we’re sorry we couldn’t find the page you’re looking for." They go a step further and give you a 10% off coupon in their store "to make things right".
That’s pretty cool.