In reply to Kemics:
Varanasi is a must.
India is not really a beach destination, as in there are much better countries for that. Also you will miss the "real" India.
Tamil Nadu is fantastic for the most spectacular temple complexes. Madurai is a fantastic city, esp at night.
Madhya Pradesh for "unspoiled" "Kipling India"
Utter Pradesh for mad chaotic Hindu cities.
Try not to move too fast; it's tiring, you're more likely to get ill, you'll have a much better experience spending time in fewer places.
Amritsar - the golden temple is much more impressive than the Taj Mahal (as are the Tamil temples)
Stay away from Goa, unless you like a more tropical version of Ibiza.
Varanasi is a must.