Have you ever had a student who has a particular interest for learning familiar tunes? The internet is becoming a wonderful resource for easy piano arrangements – which you can commonly download and print for free. One site in particular that I have turned to frequently for my students is a site called G Music Theory by Gilbert DeBenedetti. His arrangements were perfect for a student I once had who wanted to be able to play some of her favorite songs. So I assigned a few of these “just for fun” pieces for her to learn on her own. It was a big hit – she loved them.
When you visit his site and click on Free Piano Music, you’ll find that he has a large amount of music sorted by difficulty (from Beginning to Intermediate) – including some duet music. What a great resource for those adults or little ones who want to learn to play their favorite tunes!
Be sure to check out the rest of the site – there are a number of music theory worksheets and other resources available as well.
This site is a great place to send your students who are working on Classical repertoire. Personally, I’ve been able to use the NAXOS site to listen to pieces I’m currently working on, but I’ve always had free access as a college student. (Otherwise you have to pay to use it.) But ClassicCat.net is free, plus it often allows you to not only listen to the mp3’s, but often to download them also! 
Did you know that iTunes offers free downloads each week? If you use iTunes on your computer (you can download it 
Here’s a sample of my Studio Policies handout I made during my Piano Pedagogy class at college. (This one is just a sample — the info is not completely accurate to my own current studio policies.) Hope it helps in making your own!