Here's a consolidated list for the Hyatt, InterContinental and Marriott. Every code below is confirmed to work as of today. I have them more or less in order of what has worked best for me. It would be great if someone could help add to my list.
Hyatt
GE NC16700
GE International 13307
IBM 13717
Li & Fung 90010
Samsung 57039
Credit Suisse 12624
AAA 17500
AAA 15985
Credit Lyonnais 13516
Duty Free Shoppers N V 12114
Costco 13365
Bank Atlantic 79103
Senior Citizen 17497
Daimler Benz 99800
Company TVL Rate 68083
Company TVL Rate 23079
InterContinental
GE 000102806
IBM 000243132
Siemens 000104256
Ford 000103772
Federal Express 000109207
Ace Hardware 100862437
Travel Consultant IVTCD (have not used)
Marriott
General Electric GEE
IBM IBM
Siemens SIE
Ford FRD
General Motors GMC
Accenture ACC
AT&T ATT
Pepsi PEP
A few general comments:
1. GE works the best just about anywhere followed by IBM, but sometimes the Siemens and Samsung rates will amaze you. I just got 70% off at the Grand Hyatt in HK with Samsung for example.
2. I have used these probably 40 times in 10 countries and I get asked for ID 50% of the time. I have a stack of business cards I printed myself and they have worked 100% of the time. Never had a problem, even at times when I thought I may. For example, I have stayed at hotels where I got an exceptional discount to find out it was because the office was right next door (Intercontinental Beijing / IBM) and my self printed cards were not questioned.
3. I don't know about others experience, but I get upgraded 25% of the time using these codes and being "with" these corporations. I still laugh when I hear, "Sir, since you with company X I upgraded you to a suite". My best ever was a two-room suite for $81 a night (IBM discount).
4. On a personal note, this ethical debate is total crap. These hotels are obviously making money at these rates, and why should an executive of a multi-billion dollar corporation get a discount and then an individual pays more? You're leveling the playing field. If you’re still feeling guilty read this: http://en.wikipedia.org/wiki/The_Hyatt_100