1. They're free. Or virtually free. Mine generally costs me a few bucks a month in late fees and the like, but if you're even slightly more responsible than me in this area, they are free. FREE!
2. They are a wealth of resources: books, newspapers, magazines, reference materials, music, movies, children's materials, even Internet access. All right there at your fingertips.
3. They pretty much have any book you could possibly want. Even ones that are (sadly) no longer in print.
4. They contribute to the local community in so many ways: children's programming, book clubs, readers' circle, various other interest clubs, you name it. Libraries bring people together.
5. Even when you owe them money, they are still nice to you.
6. They encourage kids to become readers. Having a personal library card does wonders for getting a reluctant reader to check out some books. Literally and figuratively.
7. They bring in authors and other great speakers so that you can quietly hyperventilate about seeing your idol (like I do!) or you can learn something new.
8. They are air conditioned in the summer and toasty warm in the winter. (This may seem like a lame one, but when you're in the grueling heat of summer or the frigid chill of winter and you need to get the kids out of the house, the library is your best friend.) While you're in there, you may as well pick up a book or two!
9. They put together great thematic lists and compile book recommendations so that when you finish that excellent novel you're reading, they'll be right there with another title you're likely to enjoy. They also make magic happen when your kids are stuck on one subject (be it trains, dinosaurs, the ballet, what have you). They'll help your kids find other titles on subjects that interest them...just in case you need a break from reading Knuffle Bunny for the 712th time.
10. They are filled with people who love books as much as you do! From staffers to other patrons, you can always find someone who will love to talk books with you!
Also, did I mention that they are FREE?!