Most SHiFT and VIP Codes have expiration dates associated to them that range from a few hours to a few days. It can be cumbersom keeping track of active codes and redeeming them on time. The archives below have all known active codes for their associated categories. These categories are updated every 6 hours and "should" all be active.
Functional SHiFT Codes for the re-released Borderlands 1: Game of the Year Enhanced edition
A reliable list of functional SHiFT Codes for use within Borderlands 2
The complete list of known and active Borderlands 3 SHiFT Codes you can redeem right now
SHiFT Codes for Borderlands: The Pre-Sequel that are still active and redeemable