http://konamicodesites.com/
Awesome to see so many people implementing this bit of game history where they work.
A bit more information on the code and its history:
http://en.wikipedia.org/wiki/Konami_Code

The place for conversation that doesn't make sense to talk about in any specific game in our list. Think of General Discussion as a "catch all" for conversations about gaming, game culture or anything else worth sharing.
If you own Borderlands 2 on the PS3 or XboX gearbox has gone to the effort to fit in the konami code alog with thousands of other little things; like Micheal M (a borderlands fan that died of cancer at the age of 22) he was put in Borderlands 2 as an NPC that gives a free gun when you see him. I love how gearbox spends so much time with Pop-Culture references and eastereggs. ;p
I just Googled that, yeah it looks like it unlocks wub mode but it doesn't actually do anything. Cool they added it though, Gearbox is awesome.
Off topic: wasn't gearbox at one time associated with Valve?
After searching for it, this is the only thing I could find: http://imgur.com/r/gaming/Phv5d
Ah, they made the two expansion packs for the original half-life:
http://en.wikipedia.org/wiki/Half-Life:_Opposing_Force
Oh no kidding... That makes sense then.