Taken from http://blog.us.playstation.com/2009/12/modnation-racers-beta-now-open-voucher-giveaway-starts-today/
This was posted at 5:50pm Eastern Time so you might still get one that works.
50 More
BM44-M8BN-LFKR
L5QE-AHB7-LL89
C3TJ-JPB8-KH4N
7BM5-RCBR-5H6D
GNKR-EGBN-N4MD
593D-5MBR-EKJ8
2K6Q-ACBT-PKH6
CP3F-KQBA-KPH3
6KQJ-9NBH-EQPN
TPMK-MCBF-65TP
J297-F8B7-B3GH
8DHA-GDBC-KP7E
9QPP-TGBP-L6QN
33PQ-RCB8-AB3B
PHRP-T7BT-R64E
N844-8EBA-FD7F
QCJ3-88B5-ENLT
M8NJ-ATBQ-9RT7
QQHP-N8BL-2HR7
E75D-TNBH-ERMH
DN8N-B7BN-A9Q4
FNQF-DJB8-DR5A
MNFM-PMBB-KPK7
EKGB-QNB2-222D
DJQT-QQB8-JMH7
2H63-5GB3-FDQB
EE9E-T5B8-ECLL
KNHB-J9BF-ALC3
CH4G-ERBT-67DP
3ME6-7ABK-CMCN
QLGP-7ABR-5B4D
3H8K-J7BM-G5FP
JC7L-FNB9-BJDK
88QA-HFB5-CLPP
GGDT-QRBF-6NHL
5A8F-3FBA-Q528
MRQT-PBB7-2KLD
LGPG-E3BC-H5PJ
3ED9-QQBA-EBTM
ACL6-FBBQ-Q44F
GHLF-9QBP-DB9M
9QGF-4LB3-2GL2
CJ9E-7RBJ-57N6
N37T-L8BH-AAKH
4DTQ-JPB2-922F
P6EG-G5B4-TMEP
TMKA-QDBE-48CQ
NNJC-7PBJ-8LFA
BEL9-47B3-8K7G
A7EB-9DBJ-T62N
I took this code: 3ED9-QQBA-EBTM
This was posted at 5:50pm Eastern Time so you might still get one that works.
50 More
BM44-M8BN-LFKR
L5QE-AHB7-LL89
C3TJ-JPB8-KH4N
7BM5-RCBR-5H6D
GNKR-EGBN-N4MD
593D-5MBR-EKJ8
2K6Q-ACBT-PKH6
CP3F-KQBA-KPH3
6KQJ-9NBH-EQPN
TPMK-MCBF-65TP
J297-F8B7-B3GH
8DHA-GDBC-KP7E
9QPP-TGBP-L6QN
33PQ-RCB8-AB3B
PHRP-T7BT-R64E
N844-8EBA-FD7F
QCJ3-88B5-ENLT
M8NJ-ATBQ-9RT7
QQHP-N8BL-2HR7
E75D-TNBH-ERMH
DN8N-B7BN-A9Q4
FNQF-DJB8-DR5A
MNFM-PMBB-KPK7
EKGB-QNB2-222D
DJQT-QQB8-JMH7
2H63-5GB3-FDQB
EE9E-T5B8-ECLL
KNHB-J9BF-ALC3
CH4G-ERBT-67DP
3ME6-7ABK-CMCN
QLGP-7ABR-5B4D
3H8K-J7BM-G5FP
JC7L-FNB9-BJDK
88QA-HFB5-CLPP
GGDT-QRBF-6NHL
5A8F-3FBA-Q528
MRQT-PBB7-2KLD
LGPG-E3BC-H5PJ
3ED9-QQBA-EBTM
ACL6-FBBQ-Q44F
GHLF-9QBP-DB9M
9QGF-4LB3-2GL2
CJ9E-7RBJ-57N6
N37T-L8BH-AAKH
4DTQ-JPB2-922F
P6EG-G5B4-TMEP
TMKA-QDBE-48CQ
NNJC-7PBJ-8LFA
BEL9-47B3-8K7G
A7EB-9DBJ-T62N
I took this code: 3ED9-QQBA-EBTM