Difficulty of using foreign credit cards at Indian websites is a common complaint and I thought it might be useful to gather known info in one place.
Please post recent experiences and I'll try maintain a guide here. (My own OP has been moved to post #2.) Please include card type, bank and country of issue. If your own bank disapproved a charge, that's not the Indian portal's fault, so when possible please separate such cases.
The following is a snapshot of foreign cc acceptance at Indian websites as of December 2009, a few relevant posts are mentioned in parentheses:
Mainly, Appear to Work
^ ClearTrip (#16)
^ Expedia India (#16)
^ Travelocity India (#2,3)
^ Indigo (#2,12,31,53)
^ SpiceJet (#3,16)
^ Yatra (#50)
Mixed Reports
Air India / Indian Airlines (#16,18,33)
Jet Airways (#2,15,16,20,21,33,53)
Indian Railways IRCTC.CO.IN (#3,16,18,23,27,41,50,54)
Mainly, Don't Work
GoAir (#16)
Kingfisher (#2,9,14,16,17,18,27,29,31,38)
Paramount (#12)