to tell you the truth, dont go looking to far; your school or local public library should have some good stuff.
I found a lot of books on car mechanics and ascociated topics in my school library so i looked for books in the public one and found even more.
In addition, the site:
www.howstuffworks.com
can give you lots and TONS of ideas, those are basicaly real life situation with extraordinary simple solutions.
e.g. convertibles, windshield wipers, gearboxes, helicopters (main rotor control mechanism is amazing, good videos too) and lots of lots of more stuff like that.
Enjoy