NASA has used Ajax to redesign its website for celebrating their 50th anniversary next year. More specifically speaking it makes use of Script.aculo.us and Prototype Ajax frameworks. There are numerous features which would give you a feel of presence of Ajax, the best of which is their image gallery.
The Accordian, the tree based navigation, calender and the Ajax polls are something which you might have come across on different Ajax sites already. But the image gallery is something unique to see. It has all the images managed into sets which are displayed on the bottom. On clicking a set, the images lying within are shown in a manner similar to a deck of cards.
When you hover your mouse on above each partially visible card it becomes visible. You can click it to view to view the larger image. A full screen mode switch and a Thumbnail viewer has also been provided. Information relevant to the hovered image is shown in the right.
Overall, I liked the Ajax features implemented in the site. The navigation is user friendly. However owing to my slow connection, the site proved heavy to load. If you are curious to know how the old NASA website looked like, then have a look at this image of the old layout. From where I got the image, remains a secret. 😉