According to NASSCOM'S report the Top 10 BPO's for year 2008 were

1. Genpact
2. WNS Global
3. IBM Daksh
4. Aditya Birla Minacs Worldwide
5. TCS BPO
6. Wipro BPO
7. First Source
8. Infosys BPO
9. HCL BPO
10. EXL Service Holdings

Additionally NASSCOM said, in year 2007-08 Indian IT/BPO's recorded growth of 28% and revenues of $52 billion.

Apart from all this they presented another fact that 100 of the Fortune 500 are now present in India compared to 33 in China.
This sounds like an big story, please shout if you have any more or new update about it.