TCGPlayer - My card shop, mainly Sorcery but will sell anything I can find
eBay - Same as above, really -- though I'm not limited to cards here
Cloaker - An extension I made to persistently hide HTML elements on websites

Interesting External Links

Introducing...the Scrub - How covert contracts prevent game players from molding to the rules and improving
John Polomny - A retired energy worker who now focuses on investing from a fundamental view, weekly videos are always worth a watch