One way to keep your classroom library organized is to give each child a sentence strip with his/her name on it. When he/she goes to select a book, the sentence strip takes the place of the book they take. That way, they can easily replace the book to its proper location.

One checkout system is the old-fashioned library checkout system with pockets and cards. Put a pocket in inside front cover of every book, even your own teacher resources. Create a card for each book that includes the title, author, price, and any other important information. When a student or teacher borrows a book, she signs the card and gives it you. Keep all of the cards in an index card box with alphabetical dividers. File the cards by author, title, or student, whichever works best for you. When a student returns the book, write your initials next to her name as proof. That way if someone else checks out the book but forgets to sign the card, the previous student won't be responsible for its return.

I teach 3rd grade. For my check out system I have tried the library cards, but the kids lose them or tear them out. Now I simply place a theme book at the library center. I have a library monitor for the week.  Each child writes the date, name of book, and his/her name.  When the child returns the book it goes back to the librarian for that day or week.  The librarian will shelve the book and mark off the name.  This has worked great!

Create a check-out list for your teacher resources. When a teacher borrows one, write down the date, resource, and teacher's name. When the resource is returned, initial the entry. Keep this list with your gradebook or lesson plan book or create a file for it.

Create a check-out list for materials students borrow. Have them write down the date, their name, and the name of the book (and number.) When the student returns the book, initial the entry.

Instead of using cards for checking books out of my classroom library, I called the local hardware store.  They donated paint stirrers.  I then assigned each student a number and gave them a paint stirrer with the same number.  When a child takes a book, they place their paint stirrer in its place.  When they are done with the book and want to return it, they know exactly where to put the book back.
   

To sign out books from the classroom library: at the beginning of the school year I go to the local paint store and ask them to donate 25 paint sticks to my classroom in order to promote colorful reading with my students. I give each child a paint stick to color with crayons and markers or stickers during the first 30 minutes of the first school day. I have already printed their names on the stick with large black permanent marker. The only rule is they may not cover up their name. Then we share sticks and do get to know you activities, before learning about the library. When they want to take a book out of the classroom library, they put their stick in the spot the book was in, and when it comes time to return the book, they know exactly where it goes. My cooperating teacher shared this with me during my internship and it works quite well in my classroom also!

Appoint a student to be the classroom librarian for a day or week. Rotate through the students, or use it as a reward. Teach the student your system, then let him do the work.

I teach high school and have a lot of paperbacks that have to be frequently carted back and forth to a bookroom.  I've saved plastic red trays from when I buy a crate (24 bottles) of Coca Cola at my local warehouse store (Sam's, Costco, etc.).  These are good for carting large numbers of paperbacks, have grooved areas for handles and never collapse.  They also serve to store craft projects like the tubs.  In fact, I'm supplying the rest of the English department with my trays.