We use wordpress and a whole bunch of wordpress plugins to develop our sites. Other people are using our setup and the plugins that we develop and people have asked us which plugins we are using in our efforts. So here is a partial list which we will add to as necessary.

Role Scoper
Executable PHP widget
FormBuilder
Postie
WP Shopping Cart
GWB Ads
NextGEN Gallery
All in One SEO Pack
Simple:Press Forum