Highly recommended read. The first edition of this book, now tattered and worn, was in my pack on many Oahu hikes I did in the 1990s.
The Hikers Guide to O‘ahu: Updated and Expanded
Professor John Hall is one of the most experienced and revered hikers in the Hawaiian Trail and Mountain Club. He's also a plant expert and this book is must read for folks who want to know about Hawaii's trailside flora.
A Hiker's Guide to Trailside Plants in Hawaii
52 hikes on four islands (Big Island, Maui, Oahu, Kauai) are well described by Hawaii's trail guru, Stuart Ball.
The Hikers Guide to the Hawaiian Islands
For the historical background of many Oahu trails, this book by Stuart Ball is a must read.
Native Paths to Volunteer Trails: Oahu Hiking
Top sites
Good sites to visit to see pics and gather info about Hawaii hiking
Nandor is a good dude and a super capable hiker Go check him out if you feel the need for a hiking guide.
Hungaro Explorer by Nandor
Noah has done a lot of hiking in Hawaii. A huge array of pics available for all the hikes he's done. Impressive.
Noah Hawaii by Noah Lang
Not an extensive list but the hikes that are listed have recent reviews and tracks and lots of pics, too.