This page lists some of my favorite apps, books, podcasts, and websites. If it's on this list, I've used it for my own practice.
earplugs for musicians:
Rosindust: Teaching, Learning and Life from a Cellist's Perspective (Cornelia Watkins)
The Art of Practicing: a Guide to Making Music from the Heart (Deline Bruser & Yehudi Menuhin)
websites & podcasts:
Neil Pasricha (international happiness guru) Blog