On this page, we need:
a categorized page (perhaps driven by a reader feedback mechanism that displays the most popular appropriate proposals at the top?) of proposals. Each proposal, in a right sidebar template which is appended to the top of the wikicode for the page, has a "sign me up!" or "I'll do it!" type of section.
So, something like:
Top rated proposal Number 1: Sign Me up!
Top rated proposal Number 2: Sign Me up!
Top rated proposal Number 3: Sign Me up!
Don't see a proposal you like? create your own!