NuSapiens gives a nice introduction about recent work documenting the population genetics of India. I am very interested, as usual in the nexus between migrations and human genetics (giving short shrift to culture), and have been unsuccessfully trying to get a perspective on the India literature.
The field appears to be moving very fast. Basically the mitochondrial DNA and Y-chromosome results from India suggest ancient and yet more ancient peoples and migrations. On the large scale, southwest asia still shows mtDNA variations that appear to date all the way back to the inital settlement of the subcontinent. But the north of the subcontinent has seen substantial mixing.
Dienekes has two recent posts as well. Indus valley mitochondrial DNA and Y-chromosome studies give tantalizing hints of successive waves of settlement that may reflect specific technological developments such as farming or the domestication of horses. An earlier post links to an article using STR DNA to explore genetic diversity among south India tribes.
Also worth a look (especially in tandem with NuSapiens) is an older comment on the catalysis of the caste system by the arrival of a west Asian group.