Hi everyone. See below for a shift code for some new character skins and a custom SMG. (note the smg will be given to the first character you load):
KTCBJ-C9RTC-BSFTJ-33TT3-FBWHF

These will only be available for a short time.

On 24/03/13 there will be a new update regarding the raised level cap and a new character!

Update 23/03/12:
New gold key Shift code: WTWT3-CXSKC-9KFT3-TBBJT-ZX5FF

New Shift code
4/03/12 - KJWJ3-SCBFK-S5F3J-JBBB3-BHCJ3

C3CBT-RC3XW-9WF33-BTJ3T-SB99J
;)

KTKB3-TCZC5-9W6JT-BJBTB-6ZHTS
25 Jan: 53KJ3-CK9W5-Z5XB3-T3BJT-969KW
2 Feb: CTWBT-X5ZWC-9WRB3-BJ3B3-RWF96

I found a link to a list of active SHIFT codes on another BL2 steam group:

http://steamproxy.net/sharedfiles/filedetails/?id=121066990#7479

KTCJJ-FHZJW-W6JJB-TTBTJ-R9WWJ
WTCJ3-SHH3K-KFJT3-JBJ3J-H5965
CTWTB-JTBW5-KFTTT-JTB33-JTBWB
5T5B3-CWJSK-KRTJT-TTJJT-9HW63
WT5TB-XC5ZC-CX3T3-BBT3B-B35WB
WTCBB-H5WHC-5F3T3-TBT3T-HR6TJ
5BKBB-TXWS5-WX3BB-TBT33-3SHSB
K3K33-3W9JT-6XJJT-TB3JB-HWZZF - This code gives five keys.
C3W3B-6B95C-SWFJJ-B3BJJ-5C6XJ - Expires January 20th
KTWB3-FKX5W-HCXBB-3TBTJ-BFJWS - *NEW* (1-17-13)

Some of these are a little old, but you might still get a few new keys out of it. Enjoy!