The People's Advocacy for Trails Hawai'i has published a biking guide that describes the roads around the island. The text includes mileage, % grade, elevation gain or loss, and points of interest.
A good map of the island is published by the University of Hawai'i Press. Map of Hawai'i The Big Island is a full color topographic map of the island. They also publish a map of Maui if you plan to visit there.
I picked up a great guide book for the island. "Hawaii The Big Island Revealed" is published by Wizard Publications. The authors currently live in Hawaii - they moved there after visiting and falling in love with the place. Their love of Hawaii comes through in their writing. This is absolutely the best guidebook I've used. It's organized in a very logical fashion, and includes what appear to be very honest reviews and comments. (As an example, one review of one inn stated that you could find a better place to stay as the people that run that inn tend to be grouchy!) The publisher's web site includes updates and a password-protected area (sorry, you have to buy the book to get the password) of up-to-date reviews of places to stay. If you can't find the book in a local bookstore, the Wizard Publications web site lists online sources based on where you live (what country, that is). They also have books about Maui and Kauai.
The National Park Service web site provides information on Hawaii Volcanoes National Park. This is a good place to start if you're looking for information on the park, the volcano, and pictures.
The USGS (US Geological Survey) site contains detailed information from the Hawaiian Volcano Observatory on Kilauea, which they list as "perhaps the world's most active volcano". The site includes regular eruption updates. The current eruption of this volcano started in 1983! And of course I'm hoping it continues so I have a chance to see it. The eruption update on the site today started with "0725 March 30, 2003 Lava has spilled the breakout site popular with visitors just above the end of the Chain of Craters Road and made a run for the road itself. This morning the front of the rapidly moving breakout was within 4 m of the pullout at the end of the road, but it had stagnated. It won't take much to push it onto the roadway." And then it continues with even more details...
Additional information on the history of the Kilauea eruption can be found at the Hawaii Center for Volcanology. Some fascinating reading - that is, if you're interested in volcanos!
Information on the Mauna Kea observatories can be found on the web site of the Institute For Astonomy at the University of Hawaii.
As I mentioned earlier, I'm looking forward to getting to 2 places on the Big Island that I haven't managed to see before. I'll be getting to the top of Mauna Kea and to the active lava flows (I hope!) on an Arnott's Adventure Tour. I'll add a note here at the end of my trip to give you my opinion of the tours.
After participating in Arnott's tours: These tours are excellent, and well worth the money. Since it was a quiet volcano day the day I went to see the lava flows - I believe that if I had been on my own I would have seen the ocean entry, but not the active lava flows. I was able to see both with our marvelous lava guide Ian. And I would not have made it to the summit of Mauna Kea on my own. In addition, Arnott's tour prices are much lower than anyone else's!