I recently finished Feriana.co.nz, a simple Drupal 6 site for my fiancée and her handbag business. It uses CCK, Views and Panels 2 alpha, as well as ImageField, ImageCache and Lightbox2 modules. I also wrote Image Themer and Views Themer modules, which I contributed to the Themer package and plan to abstract in to re-usable solutions in my next Drupal 6 theming project which I start this week. I will also be demonstrating these modules at the Advanced Theming Techniques session (if it gets in – Go Vote!). You browse the still-very-alpha code for these modules in Drupal's CVS repository.
Xero is another accounting application that competes with the likes of Quicken and MYOB. It isn't the first application-as-a-service in this market, but it is, IMO the best.
There are several efforts around to collect links and summaries of drupal sites. This is by far the most comprehensive I've seen so far. Sites are categorized by region and other useful terms; http://www.drupalsites.net/