Ninja 250 Rider's bookshelf
A Twist of the Wrist II by Keith Code (This one is for street riding. The original TOTW is for racers.)
How to Ride a Motorcycle by Pat Hahn
Sport Riding Techniques by Nick Ienatsch
Smooth Riding the Pridmore Way by Reg Pridmore
If you don't have a copy of the owners manual, you can read it for free at kawasaki.com. You should be able to download it or print it out. It's not in one big pdf file, though; it's in about 17 smaller files. Open up each pdf, then save a copy from Adobe Reader by using the "floppy disk" (save) icon. You can also print it directly if you like.
To get there you have to jump through a few hoops. Once you're at kawasaki.com, go to Owner Info --> Owner's Manuals, then click through a few screens to your year of bike, then click Owner & Service Manuals. You'll finally get to Download Manual. It's the same place you go if you want to buy a Service Manual.
Maintenance and Repair
Important Copyright Notice: The Kawasaki manuals below are only available in paper version. There are no legal copies to download. Besides being illegal, these electronic versions are often incomplete, missing entire pages with important information. They're a waste of your money. Please, purchase the official copies. You can tell them by the price. A Service Manual and Supplement for the EX250F are about $35 each. An EX250J Service Manual is about $65.
Other interesting reads
Zen and the Art of Motorcycle Maintenance: An Inquiry into Values by Robert M. Pirsig
Ghost Rider: Travels on the Healing Road by Neil Peart
Perfect Vehicle: What It Is about Motorcycles by Melissa Holbrook Pierson
Jupiter's Travels by Ted Simon
Long Way Round: Chasing Shadows Across the World by Ewan McGregor & Charley Boorman
Long Way Down: John O'Groats to Cape Town by Ewan McGregor & Charley Boorman
Motorcycle Camping Made Easy by Bob Woofter
Blue Highways: A Journey into America by William Least Heat-Moon isn't moto-related at all, but it suits the vagabond spirit.
Blood, Sweat and 2nd Gear: More Medicine For Motorcyclists by flash gordon, m.d. covers medical, health, and emergency tips for motorcyclists.
Deck The Halls - a carol by ATG
Where to buy
Whitehorse Press sells many different kinds of motorcycling books.