In steam click Add A Game, then activate a product. Keep trying codes until you get one that hasn't been used.
04YTN-QN868-EDCA0
EJKD9-I6PIZ-3DXHF
470HC-MIFBI-HF0MB
9ATEE-CTA5F-KP7TG
HBJI4-MNLBK-IMMRD
52725-M39ZN-8B6M0
ITYGG-787CM-PRAVZ
L80IG-ZTMWV-50GAI
AJE6W-TH4T3-H9TFQ
TC9GF-DVW2Z-BWBCA
BVLLX-JGLAI-7HYR5
CTFYH-BWKMT-8CFRV
B3FV5-AJQP0-3LNTW
P3PG2-WTF2N-2Z0FE
F92LA-5AJVA-ZIX9Z
GXRT8-WXCJ7-28TFG
PMPDP-DZKV2-QGPAV
L6AYD-0TZ5Q-WVWEA
R8TTR-E5HG2-D6RHE
PL5ZT-MQJ9I-QRJNH
0WHD7-N58PZ-IFN7B
VY5LK-ECD3G-6H4G9
NKRPQ-02CM7-KKZG0
8LLGY-LWK5M-CQ70B
VANQE-3EJMC-4LZVT
GIB59-YQ3HX-ZH7QP
ECXKP-M5MDG-MCPYB
KKFJE-DB4Z3-F42Y2
IFN7G-Z8WN7-F32EI
IAPDX-JF5CG-34K3H
C4VKN-QF6NF-53YDZ
CMPMF-WA5W6-LBVER
4E3YE-PVRZL-ZTQ0M
R46XA-43RT5-2HRQ5
PP447-056LZ-CXD9W
A0IJ6-T4GMM-5XYA3
P34YR-A8CG0-8C7V5
6JP2L-62ETQ-THAEZ
WK5RV-GPXGH-KLG3B
KDAMK-WHI6R-C8493
DF5KR-PQWTK-XXEYT
HDW4X-FAVXB-57VXE
L47W2-VJVH0-YFB9C
TF8CL-VBDMI-YHY0C
6X4EY-J89D0-N9249
0EKBL-9L3JX-R6VQA
CNEGB-BMGBI-DQ4NC
8PF8X-7VXPP-BRGBL
LH9MB-6EZ3B-PJFEI
CN2RZ-KLP83-GB44T
EDIT: MOAR KEYS
P8QA9-KKBTI-EXRIZ
JM2AE-GNKV4-IEJ4F
RWF9X-FZ8WG-YZ8W0
0GPG5-932VE-CHMPL
Q5N9R-6VJBC-FBDPT
JDWLZ-GNX2Z-C7PN5
V73DH-B3WLA-IDAKZ
Q2BQZ-7TI0C-WDDIV
QVMI4-KJ3BB-38EML
F8EHD-JKJIN-HR2CY
ZNA3J-9AEKV-DNHPZ
NTFE3-R8QXX-LKYEJ
7KRNQ-N2F7I-J34GK
X4BTD-KHC8L-AGPY7
DBKIH-577AV-GZ0Y3
0FBNF-CVNG8-333NP
WGM5V-2ATR3-FJACK
GTG9M-KI7GB-YEDT4
F8Y6F-8Q3KT-KDITE
8X0X7-4MTJ0-XPCVK
GFGDZ-BQCIQ-4HJCP
HDIA3-TM83X-Y4AR2
T6RXB-MA9LF-5WKA4
5YF8B-52J35-3GBVK
4CV2X-QCYMP-F8K9Q
34RBB-L5HQJ-W490G
CR7KN-E4WK4-XDK45