Check out http://www.homeprintstudio.com - my latest OpenCart store.
It is full of nice extensions, some of which have been rather, err 'tweaked'! A couple worthy of mention are the 'manufacturers slide' - which now shows the 'Designers' (sellers)! Also the watermarking, which works on jpgs, and gif images - something that has proved difficult to do reading posts on this forum! I could list all the extensions but it would take too long.......

The main difference with this store is that it has been comprehensively customised to build in a system to allow buyers to become sellers and upload and sell their own digital downloads (craft sheets in this case) and receive a commission from site owner on each download sold. Buyers can become sellers by 'applying' to become so from within their account area. Once approved, they get a nice new account area with enhanced features.
So, the seller has their own upload and edit area together with earnings and payments system so that they can see just how many of their downloads have been sold and how much commission they are due! Of course this is all captured. replicated and controlled from within admin.
If anybody is interested I will post additional images showing the custom areas.
The site went live last night (19th February 2011) so it has only a few downloads so far.
Please tell me what you think.