Ned's is an independently owned bookstore across the street from the Cal campus, on Bancroft. I'd typically compare prices on books at multiple stores to see who had the better deal. While occasionally Ned's didn't carry a book for a certain class, they almost always did, and their prices were very competitive. Quite frequently their prices beat those at the ASUC (or A-Suck to many Cal students) book store.
The staff was always very helpful. Whenever I had trouble locating a particular book, I was able to find someone who could help me. They were always quick and courteous.
Some areas of the store are kind of cramped, so be prepared to have to squeeze around people blocking the aisles because they are staring blankly at the 20 books they're going to have to buy for just one class.
Ned's also carries a selection of other supplies, like blue books, pens/pencils, study sheets, and more.
Plus, they buy back your books at the end of the semester, and offer good prices for them.