My website has a review of all the main books that are revelant to the region. Howell and Webb is by far the best guide to the region. However, it only goes as far as western Honduras, which means that if you visit the eastern parts of the country you will need to use the Costa Rica guide by Stiles and Skutch. Personally, I consider these the best guides to use, but some people may prefer Ridgely's guide to Panama, which includes Costa Rica, Nicaragua and Honduras, whilst some people prefer might prefer Peterson or Edwards, which are both really aimed at Mexico.
Unfortunately, most birders just visit the western parts of the country, where they only need Howell and Webb. Travel is far easier here and the birds are better known. Further east there is a very real chance of finding something important - on one of my recent visits I saw what could possibly be a new species of Wren and I have found several new species for the country in the past year or so. If you are planning some serious birding, I recommend that you take both of the above guides. If you are unfamilar with the migrants, you may also want a North American guide. That's a lot to carry if you don't have your own transport, but they could be very useful if you find something important.
Feel free to contact me directly if you need any information. I am regularly in Honduras and may even be there when you are - trying to net a wren.
Tom