I have found Lonely Planet to be a superb choice. While I have not taken the India/Nepal tour, I have taken 5 other Tauck tours and found that LP has a lot of good info
I'm a fan of Eyewitness guides. Beautiful glossy photos, maps, history, trivia, etc. They can be a bit heavy for carrying on tour but wonderful for reading up ahead of time.
We also love the Eyewitness books. Sometimes, we've Xeroxed pages to keep the weight down. For some cities, there are books dedicated to that particular city. Also, in some cases, there are smaller books called Top Ten for a particular city which are much easier to carry with you. Most of them can be purchased on Amazon. Rick Steves also has very good guides
There are various best travel books available on Amazon like Little princess, Annapurna, Lonely Planet Nepal, Lonely Planet Trekking in Nepal, etc. But if you want to go only for the purpose of travel, then you can go with the book Lonely Planet. And for more details about travelling and trekking you can also visit here.
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I also pick up used travel guides in thrift stores cheap. Sometimes 25 cents. Then tear out pages to take with me.
Then of course there's the public library. Helps me decide if a guide is worth buying.
There are various best travel books available on Amazon like Little princess, Annapurna, Lonely Planet Nepal, Lonely Planet Trekking in Nepal, etc. But if you want to go only for the purpose of travel, then you can go with the book Lonely Planet. And for more details about travelling and trekking you can also visit here.
Careful, do not click on Rajesh link!