To redeem keys simply click "Extras" from the main menu and choose "Shift Codes" from there a new UI will open up. After that click "Shift Codes" again at the bottom and a new window will open up where in you enter the key.
NOTE
You can copy and paste the key using CTRL+C and CTRL+V this will save you a lot of time because instead of typing it all out, you can just use the simple method! TO KICK ASS

These keys are ones that will 100% work as a commenter told me that some of the keys in the next section have expired.
5BW3B-F96CT-KXJFK-TB3B3-39BWZ (20 keys) 03/07/2015
W353B-9FXZZ-RBJ3J-BT3B3-JK9KH
KBC3J-95WXF-WBSBT-TTJJB-KTC6K
CTWTB-JTBW5-KFTTT-JTB33-JTBWB
5T5B3-CWJSK-KRTJT-TTJJT-9HW63
KJ5BT-FBKSK-KXJ3T-3BTJT-FJX5C
K3K33-3W9JT-6XJJT-TB3JB-HWZZF
WTC3B-Z5ZWC-HW6JT-JJJBJ-9FWXR
K3WJT-BFBRW-S5RTT-TBBB3-9XWZ5
KB53J-RW5XX-539BT-BJT3J-CC55T
WB5TT-JFCXX-CBS33-TTTBJ-JJ95B
K3CBT-CRKR6-CB9BT-T3TBJ-595J3
CTC3J-KR9H5-WTZ3T-TJ3TB-6SRRJ
WBCTT-XX3RK-HK6TB-TTTTT-B5Z53
CJKJB-XWBR6-WJXKJ-JB3TB-WTCWX
CBCB3-SW36X-KJXW3-TTT3J-SFBSB
C3WBB-W3BRR-5J6WB-3JJJJ-35ZKZ
KTK3J-JWT6X-KB65T-3JJ3J-WHBRT
CJ5B3-6TTFF-5365T-TBJBB-SKTCB
W3CTJ-BFTFR-KJRK3-JJT3J-H6H36
5B5TB-XFBX6-WBXWJ-JJ3TJ-9RXZW
53K3T-JZJX6-WBXKB-BBJJB-SJH3K
C35BJ-SRBF6-5TFKB-BBTJT-FSBZK
5BC33-CRJRF-WB6WB-3TTTB-655ZX
CT5JB-FSTFX-5TF5T-3JJTT-6CF6T
WJW3B-5HBR6-5BXCT-33TJ3-WXT53
535TJ-3JC6X-KJXCJ-BTBBT-K5WFR
5JWTT-KHTSB-S5TXC-BB33J-HCJ6K
CJC33-RH3ZB-9KTX5-3T3JJ-SXFRK
KJ5BJ-H9BHT-HCJ65-33JJ3-HTXZZ
K353B-TWSBX-H5BR5-J3T33-6XTCK
WTKJ3-9JXZ9-6TJJB-33T3J-FRJC6
KBWJJ-WTXB9-C59J6-WFBTJ-TK6BJ

Please take not that there is a 255 key limit resulting in keys being wasted if redeemed when you already have 255 keys. I suffered from this myself as I just entered all the codes one after another and didn't pay attention to my key limit.

These are keys that have been commented about in the comments section, they will lack of information and probably not work, but hey they could lead to more keys!
If one of these keys doesn't work then feel free to say that in the comments section and I'll remove it from the guide.

WBK3T-BKW6T-TXTRK-JTTBT-C6BS5 (05/07/2015) 25 Keys

KB5BJ-WCRZ9-6J33J-BBJ3T-XK96K
5TK3J-CFWK6-9KTXK-TTTJB-J56X6
K3WTT-TKRH9-X3BJT-BJTBT-KXTSB
C3CTJ-XJ6HZ-FJTTJ-JBBBJ-3WTJZ
W3KJJ-KJXHZ-6JJBJ-3TT3T-33XBR
K3CB3-3JF99-RJ3JB-JJ3JJ-BT3RX (Thank you UltimateX for these codes)
K3WBT-Z95HZ-FTT3J-BTTJB-ZFX63
CBC,J,B-K9WHH-63JTJ-B3JJB-HT533
WTCTJ-J9CS9-RJJ33-T3J3B-BT9XH
CJWJJ-HR5Z9-6JT3J-J3TBT-6TJ6K
5BWBT-RX5ZH-FJBJB-JBTJT-CRBWX

Thank you for taking the time out of your day to read this guide, and as usual please rate up and favourite!

I'm afraid i won't be adding to this guide any further, at it's current time it has over 300 keys available and i can't find the time or motivation to update it every time like i have been. If you would like some more codes feel free to look in the comments of this guide or look at other guides made by brililant people. Thanks again for all the support it truly means a lot to me and I'm glad I helped a lot of you fellow looters!