said 10 months ago:
Use Ecwid: http://www.ecwid.com. It will work with any theme since it pulls in the shopping cart via a cloud network. It’s very well thought out, easy to use and just plain wonderful. No need for an SSL cert. either.
It uses a free plugin and a thrid party free Ecwid account but you get better options with the paid service for $17/mo. like SEO capabilities and discount codes, etc.