Not sure if any of you have seen the site or not yet, but it is pretty awesome. It has a stock market-esque page ( https://www.echomtg.com/market/ ), it shows price histories, and it even allows you track a collection, including the amount you spent on each card, current prices, gain/loss percentages, etc. The free version allows you to store 150 cards, but premium accounts (for $2, $3, and $7 a month) afford you a lot of cool functions. I am using the "Seasoned Collector" level for $3 a month and I love it.
I'll check it out. Thanks for the 411