Hi, many people have asked for a e-commerce plugin. Apart from the ministore and the OS-Commerce plugin (with some problems) there's still nothing. There is a new E-commerce plugin for Wordpress available at
http://www.instinct.co.nz/e-commerce[*1] , the developer of this claims that it might be quite easy to port it to another system:
We are also very open to porting WP e-commerce over to other platforms. Its architecture makes it extremely portable (for a WP plugin).
I'm no developer (far from that..), but if you're a developer and about to start making your own E-commerce plugin, this might be something to consider.