Although out of print, you can still find it used as well as new in some book shops in India. In addition to treks, Trekking and Climbing in the Indian Himalaya, covers many trekking peaks as well as a couple more technical ones. I used this book as an outline when I climbed Chamser Kangri in Ladakh. The practical information is pretty brief on the treks and climbs themselves and there is a lot of extra nonessential information and pictures that makes it pretty heavy to trek with, but the book covers some interesting routes and peak not covered elsewhere.
Decent book and really the only option for treks in India outside of Ladakh. Maps are useable and better than most you can find in India. Descriptions are brief but adequate. I've used the book quite successfully on many occasions, so for the treks it covers it does the job.
Lonely Planet is still probably the best guide book for logistics in India though I find it seems to get worse with each edition instead of better, and its monopolistic popularity mean that any place mentioned in the book is likely no longer a good deal when it comes to accommodations. Still when it comes to the nuts and bolts of getting around, maps ect, LP is still probably the way to go.
Himachal Pradesh is another of India's major trekking destinations however there is none of the lodge infrastructure that exists in neighboring Uttarakhand so most treks are camping only. There are a few homestay trekking options in the Spiti Valley, as well as the pilgrim trek to Manimahesh Kailash in the Chamba Valley during the pilgrim season.
Having spent nearly four years in the Himalayas, much of it independently trekking throughout the region, I thought I would help others by sharing how to trek independently and economically in the Himalayas. Its not necessary to spend $30 to $70 a day through a travel agency in order to enjoy the splendor of these mountains as many people seem to think. All it takes is a bit of self confidence and knowledge.