Found out about this today, and had to get in the game. I have played a lot of Magic the Gathering and Hearthstone in the past...so this is right up my alley.
There is a fully detailed post if you head over to the Trending page...a game made by 
Here is my most valuable card I pulled from my booster packs today:
...and this being the second most valuable:
Purple is 'epic' rarity and yellow is 'legendary' rarity. The other two are blue 'rare' and gray 'common'.
Looking forward to the Beta (game is in alpha currently), and actually getting to play.