Can't live with 'em, can't live without 'em.
Love them or hate them, travel guidebooks are very much a backpacking essential, increasingly dictating to whole generations where to go, how to get there and what to do.
All over the world you can see twenty somethings - and increasingly older - often desperate for succor, with their heads stuck in guidebooks. Reading, re-reading, desperately trying to find the best possible routes and the best possible places as if encoded somewhere in the pages.
The problem is everyone is doing the same and generally reading from the same text, which means less people are striking out on their own or making use of local tour guides.
That said, you'll probably need to pick up a guidebook at some point, so here's a quick rundown of the most popular and useful brands:
AKA "LP", "The Book" of "The Bible"
The most ubiquitous of all guides, often with solid information, but not always up-to-date. They do cover some interesting locations (the Caucasus, Iran and Syria for example) but their shoestring titles are often appallingly lacking in depth and information-- it all depends on the edition and author. However, their maps are probably the best of all guides. Newer titles are now published in a jazzy format (with questionable 'authors choice' recommendations), but can be better than older versions.
Maybe the most in-depth and informative although their structure can need getting use to if you have only previously used other guides. RG doesn't cover as wide a range of countries as LPs and older titles are nowhere near as good as newer ones, which are first rate in most cases. European guides are excellent and their alternatives to other popular titles (i.e. LP's India/Thailand) are a great alternative to get away from the crowds.
The best of the bunch (besides Rough Guides) if you can find them especially for African countries and off-the-beaten track books. Bradt guides normally avoid the most popular destinations and going head-to-head with the big-boys of the industry. They can suffer from being out-of-date, having fewer updates (but a few years out-of-date should not worry you), and have a somewhat amateur look to them compared to LPs. Highly recommended.
New editions have a new format and look a lot smarter, but are less budget focused and often have a slant for Americans as they are written by Harvard students.That said, they are some of the most accurate, being updated yearly. These guides are perhaps best avoided in regions with many young American travelers.
An excellent series and perhaps the only multi-country guides worth having. The South or Central America Handbook is a serious project and puts the Lonely Planet and other versions to shame. In addition, they publish many region guides to specific [regions] areas within large countries (for example India). Footprint authors do on occasion rave about places off-the-beaten track that when you arrive can be less than inspiring. Equally poor town maps and readability are their only other let downs.