Reliance - They have unlimited plan for data card - Rs.1500+tax per month. I use it for the last 2 years. Speed is like 80-100 kbps
*www.reliancecommunications.co.in/Communications/Netconnect/netconnect_tariffs_details.html
Tata - No unlimited plan, 1500+tax for 5 GB cap. Other plans very similar / same as Reliance
*www.tataindicom.com/t-business-data-plug2surf-tariff.aspx
BSNL - If you have BSNL CDMA coverage near your place, you can try it. You need not even buy the card, can go for retnal. Total will be 550+tax which includes voice rental + data card rental + unlimited internet. I am currently using and testing it.Speed - 80 -100 if tower is near, 60 or less if you are far away from tower.
*bsnl.co.in/newsdetailed.php?news_id=370
From my experience, all data cards speed depend mainly on the distance from the tower. So decide based on the tower distance, thats my suggestion