Sometimes when I stumble on some nifty things that relates to Steam Trading Cards I will add them down below.

• Grimm (Notice: Grimm is no longer available on the Steam store. )
• The Descendant

• Steam Trading Cards
  • Official Steam Trading Cards group (created by Valve, administrated by Valve employees)
• Idle Master
  • Official Idle Master Steam group (anno 2014)
• Badges Collectors
• Card Trades

• Steam Tools Hub
  • Lets you find cheap badges to craft and sort your inventory by value
• Steam Card Exchange
  • Easily preview badges and backgrounds, and allow automated trading with their card bot.
• Steam Ladder
  • List of the highest level Steam profiles and other related top ladders