If you buy anything on Amazon, please consider choosing a charity first from this link:
http://smile.amazon.com/

1/5 - 1/31
$6 ($1 after EC) Ace Patrol Bundle
$13.19 ($8.19 after EC) Bioshock Infinite
$15 ($10 after EC) The Bureau: XCOM Declassified (pricematched until 1/27)
$15 ($10 after EC) XCOM Collection

1/23 - 1/31
$7 ($2 after EC) GTA Trilogy
$7.49 ($2.49 after EC) Max Payne 3 Complete
$11 ($6 after EC) GTA Trilogy + GTA IV
$8 ($3 after EC) LA Noire + Max Payne 3
$8 ($3 after EC) GTA IV + Max Payne 3

1/24 - 1/31
$9 ($4 after EC) Tomb Raider
$7.49 ($2.49 after EC) Thief Bundle
$7.49 ($2.49 after EC) Legacy of Kain Bundle
$15/$18 ($10/$13 after EC) Final Fantasy XIV/Collectors Edition (Not Steam)
$13 ($8 after EC) Hitman Bundle
$7.49 ($2.49 after EC) Hitman Absolution

1/26 - 1/31
$8 ($3 after EC) Battlefield 2142 Deluxe (Origin)
$7 ($2 after EC) Burnout Paradise Bonus Vehicle Pack (Origin)

1/27 - 1/31
$8 ($3 after EC) Mirror's Edge + DLC (Origin)

1/31 ONLY
$7.49 ($2.49 after EC) Dark Souls (Extended to 2/1, EC also extended)
$7.49 ($2.49 after EC) Enslaved + Inversion (INVERSION IS REGION LOCKED TO AMERICAS, Enslaved doesnt work in Japan)
$20 ($15 after EC) Naruto 3 Full Burst

Not sure about dates
£10 Borderlands 2 GOTY (UK only)

The others

FAQ:

What are EC credits?
Editor's Choice credits are $5 promotional offers that could only be obtained in the months of November and December for purchases in the Digital Games Store.

Are these credits stackable?
No, one per purchase only.

What items do these credits apply to?
Anything in this list

Can I transfer credits to someone else?
No, they are tied to your Amazon account.

How do I check how many credits I have?
Unfortunately, there isn't really a way to check on Amazon . You need to dig through your email and keep track of how many you have used.

Warning

The following games are region locked. Click the links and examine "AllowPurchaseFromRestrictedCountries" and "PurchaseRestrictedCountries" before you purchase to ensure that the key will activate in your country:
Dead Island
Dead Island GOTY
Dead Island Riptide
Metro Last Light
Saint's Row IV
Inversion
Football Manager 2014 (Restricted in quite a few countries)

Source
Archived Threads: 1, 2, 3, 4