Most of the regulars here move around a lot and it benefits to be well informed about the various offers available from various travel sites.
So I request all to please post any offers known to you for the benefit of all.
Heres a few that are presently on

Cleartrip
Book a SpiceJet flight before March 31, for travel before April 15 – and get 50% cash back on the base fare subject to max. Rs.400 for less than 750 KM and Rs.800 for more than 750 KM.All taxes and fees are payable in full. Tickets booked for infants cannot be included. Offer valid only once per credit card.

Book an Indigo roundtrip before 31 March, to travel before 19 April – and get Rs 800 cash back. All the taxes and fees are payable in full. Tickets booked for infants cannot be included to avail the offer. This offer is not applicable on combination of different airlines for any sectors.

Book GoAir flights before 31 March, for travel before 15 April 2009, and get 50% cash back on base fare only, taxes payable extra. Tickets booked for infants cannot be included to avail the offer.

Ezeego
Book a Spicejet flight before 31st March, for travel before 15 April 2009 and get 75% of the basic fare or Rs. 750/- per sector, whichever is lower as Cash Back.

Book a Kingfisher Airlines flight before 31st March using ICICI Bank Credit or Debit Card and get 10% to 30% Cash Back on basic fare.

Book a JetLite and IndiGo flight before 31st March using ICICI Bank Credit or Debit Card and get 10% to 100% Cash Back on basic fare.