Hoping for plenty of interesting suggestions, here are mine (from quite small viewing pool):

1.Apu trilogy (Ray, 1955-9)
2.Pakeezah (Amrohi, 1971)
3.Cloud-Capped Star (Ghatak, 1960)
4.Charulata (Ray, 1964)
5.Days and Nights in the Forest (Ray, 1969)
6.Paper Flowers (Dutt, 1959)
7.Mughal-e-Azam (Asif, 1960)
8.Baiju Bawra (Bhatt, 1952)
9.The Music Room (Ray, 1958) 
10.Awara (Kapoor, 1951)

So, Mother India didn't make it, though it's a long time ago i saw it. Pyaasa and Sholay (the dvd i found available is expensive) are top of my must-see list. Need to see some by Sen + Benegal, and pre-WW2 classics like Devdas and Sant Tukaram among many others. Not greatly impressed by any of the recent popular films i've seen. Mira Nair came close to the 10. I may give Ghatak's A River Called Titash another chance; i loved the opening, but became increasingly bewildered and alienated. It may well be a great testing masterpiece, in what's certainly a very rich, unfairly neglected cinema tradition. So much still to explore!