http://www.zerodha.com/
is new and cheapest, they from BLR. Next is RKG.
But mind you cheapest does not mean, huge profits. There are two type of brokers, one who provide services like tips, research report reports, analysis, better trading software, customer training etc. They don't charge anything for these services, they add all cost in brokerage and so the brokerage is high.
Vanilla brokers like Zerodha, RKG gives no services except trading terminal.
If you have own ability to make calls what to buy and sell at what time then Vanilla brokers are best for you. If you don't understand that, then please do attend some proper training from BSE training institute, NSE -Manipal courses.
Remember only 2% people make money here, rest all make losses.