My primary instrument is voice, but I also teach piano to my voice students who are seeking to enhance their musicianship and reading skills. Piano is an excellent way to learn to read music and learn music theory. I recommend it for voice students as an added tool to help you become a better musician or for anyone who wants to begin to learn more about the wonderful world of music. Often my students take voice and piano lessons back to back.
I use the Alfred books for school aged students, which can be found on amazon
For adult beginning piano students the Alfred's basic adult book will help you learn how to play at an accelerated pace.
For children Alfred's has a wide range of books for all ages: Piano books
If you are in need of a piano to practice and play on I recommend this site: Piano adoption