Madden Cards:
There are 281 total Madden Cards this time around. Player cards give that player a boost for a specified amount of time (based on the type of card--bronze, silver or gold). Playing a Coach card boosts your team awareness for a specified amount of time. Stadium Cards unlock stadia for exhibition mode. Historic Team cards open those squads for exhibition, and Cheerleader/Pump Up Crowd Cards give your team a temporary boost. Here are the card categories, and how to gain the locked Cards within each:

Player Cards: #1-155:
The following cards are unlocked by completing Mini-Camp challenges (the rest can be gotten by purchasing packs of Cards with Tokens):
#2: Unlock by getting gold in the All-Madden Chase and Tackle drill.
#30: Unlock by getting gold in the All-Madden Coffin Corner drill.
#38: Unlock by getting gold in the All-Madden Ground Attack drill.
#42: Unlock by getting gold in the All-Madden Precision Passing drill.
#52: Unlock by getting gold in the All-Madden Swat Ball drill.
#99: Unlock by getting gold in the All-Madden Trench Fight drill.
#104: Unlock by getting gold in the All-Madden Clutch Kicking drill.
#147: Unlock by getting gold in the All-Madden Pocket Presence drill.

Coach Cards #156-187:
These Cards, when used, raise your team's awareness for a specified amount of time.

Cheat Cards #188-219:
Cheat Cards, when played, produce special game conditions for a specific amount of time, based on whether they are Bronze, Silver or Gold. Certain ones need to be unlock via Mini-Camp drills. They are:
#195: Unlock by getting gold in the Ground Attack drill.
#197: Unlock by getting gold in the Clutch Kicking drill.
#199: Unlock by getting gold in the Swat Ball drill.
#208: Unlock by getting gold in the Pocket Presence drill.
#209: Unlock by getting gold in the Trench Fight drill.
#210: Unlock by getting gold in the Precision Passing drill.
#211: Unlock by getting gold in the Coffin Corner drill.

Stadium Cards: #220-224:
Unlock these Cards, and you'll unlock the stadiums, and make them available for exhibition games.

Historic Team Cards: #225-249:
Unlock these Cards to make the Historic Teams available at the team select screen.
Cheerleader/Pump Up Crowd Cards: #250-281
These are unlocked by completing each team's Situation in Mini-Camp mode, with the exception of these teams:
#251: Cincinatti Bengals
#260: Dallas Cowboys
#264: San Francisco 49ers
#273: St. Louis Rams