Disclosure: Shameless plug from a team member of yet another travel search Startup 90di (which mainly searches for flights, trains, buses in India). *
Seeing what Adioso has done, and also that there is a good deal of overlap. Could not resist, telling about our Startup.
We do what we call as 'free text search'. Its customized for searches in India, like you can do something like:
'Bangalore to Kanpur by train via Delhi'.
Or you can just search by a train name, or number, or flight number or by Airline name and many other things.
Some more examples of free text searches possible are at: