Already described this site on my blog (with video clip), but here's some more technical details.
The site in question, ComicJuice.com is a comic mash up tool: visitors build comic strips with panels and bubbles, based on images on the web. A lot of effort has gone into elegance and usability, as well as the use of recent technologies online. Because of this, Internet Explorer is not supported.
The site is built on Drupal 5 and features loads of custom code (mostly JavaScript) to make the comic creation and viewing work. Noticable is the use of <canvas> for the (procedural) speech bubbles. The modules used are all quite simple. Aside from core, there is Views, Tagadelic, Pathauto and Akismet. The theme is a heavily modified Garland, with almost all the images replaced and some layout changes in the content.
I used jQuery 1.1 and Interface as the base (with the jQuery 1.0 compatibility plug-in for Drupal core), I basically just started building out all the different behaviours until it slowly came together. First I built the bubble model, made it resizable, added the sliders, etc. Debugging tools like Firebug were a life saver here for figuring out browser quirks.