For general travel information I buy used and therefore old editions of Lonely Planet, Frommers, Fordor’s and others.
For example, the Friends of the Tucson Library has a book sale several times a year. The Fodor’s Panama copyright 2008 cost me $1.00. The places I want to visit hopefully are still there and in the same location — otherwise this was a bad purchase! I use these older editions to get a sense of where I want to go, what I want to see and do, and to set a tentative itinerary and time line for my travels.
When I get serious about taking off I them purchase the latest edition of whatever travel guide I believe is the best. And the best in my opinion is almost always Lonely Planet.
The only issue I have with Lonely Planet is every once in a while it takes a cheap shot at the United States. I just skip over these and mark it down as jealousy.
For those who are serious about keeping the weight of their backpacks/suitcases light you may want to entertain the though of tearing out the pages of the book for those locations you are going to visit and leave the remainder of the book at home. Or take the entire book and after visiting an area tear those pages out and leave behind. Yes, Nancy and I have done both.