No doubt on this that top companies visit the IIT's for placements. Companies like Google, Flipkart, Facebook, Amazon etc come for student selection with excellent packages being offered.

The placement in IIT's may vary and also depends upon the specialization you are interested in. In general, one can expect a package of approx 10-30 lakhs per year depending on various factors.

Let me know if you want to know for any specific IIT.