This guide has a lot of useful information but as it was published in March 2003 it is out of date.
The quoted prices are likely to have gone up slightly and some places to eat or places to stay may not be there any more.The section on Budapest is detailed and useful. Most of the information on attraction opening times seem to be correct (even if the prices aren't). I only visited the capital so I don't know how good the information on the rest of Hungary is.
I recommend this book if you are travelling to Hungary but be aware that it is two years out of date. I couldn't find any other guides that weren't even more out of date.
If you visit Budapest I recommend a tour of the parliament building. If you are an EU citizen this is now free. Remember to take your passport with you to prove your nationality. Otherwise it is still cheap (approx 1400 Ft/4/US$7.50/6).
There may be additional English language tours to the ones specified in this guide. Go to the ticket office early in the day and ask for details.
Also recommended is a trip to the baths in Budapest. There is a detailed list in the guide, but make sure you read it carefully as some baths are open to men and women on different days. Prices have gone up slightly.