I came here looking for the same, as I run a web hosting company and it sits on the side well i do Internet marketing on my other site that offers seo and stuff, So i was thinking of adding a web hosting offer to my visitors too. Most of these require whmcs. there has to be a plugin or its time to dominate the industry with one. The problem is, of word-presses own platform. you would have to set a page up, enter your own coding and sale buttons and so forth. Wou,ld be much more easier just to have it connect to the server set the account up with all the details shoot the customer a welcome maile and your done. easy moey.. see why we need the plugin.. rock on glad i found this page.
WHMCS is amazing. Best thing is if you buy a reseller account on HostGator you get WHMCA for free.