Most people want to deal with established organizations when they work or volunteer abroad. This is great for security and consistency, however you may want to consider finding your own space to volunteer. Research (guidebooks, guidebooks, guidebooks!) the location you are going to go, look for a cool town you want to exist in, and seek out the organizations that are close by. Then just call them up and see if you can work for them. Most will exchange food and lodgings for work.
Formal work is okay too - consider organizations such as Americorp, Teach for America, the Peace Corps, or the Jet Program. These are all reputable programs you can trust to send you somewhere to work - but note that you are often responsible for your own expenses, and they may or may not pay a stipend.
Informal work opportunities could be through WWOOF, or something creative like teaching English to monks. Whatever your strength - and whatever type of work you feel suited to do, from farming to teaching - chances are, there is an organization in your desired destination that could use your skill set. Don't be afraid to reach out!
Speaking of guidebooks - check out Lonely Planet. In terms of reliability and applicable materials, they win out as one of the best guide books on the market. As a bonus, they have a book - and a section on their website! - for nearly any destination you can think of.
As you're researching, think about what kind of experience you want. Do you want to be there for a week or a month? What kind of work are you willing to do? Are you there to experience the culture as a local would, or are you looking for tourist stops?