Major Players
- Easy Digital Downloads (EDD)
- WP eCommerce (WPEC)
- WooCommerce
- iThemes Exchange
EDD
Built with template files similar to a standard WordPress theme
WPEC
Again built with a bunch of templates like a standard WordPress theme
Nice admin feature that will move the templates to your theme
WooCommerce
More like Genesis than a 'standard' WordPress theme
Lots of hooks all through the templates
Take a look at
- archive templates for each
- my account/history templates