Recently I revisited a technique I used in college to decorate my dorm room walls: letters cut out of fabric and adhered to the wall with liquid fabric starch. Want to freshen up your wall? You can peel these letters off, wash the wall, and start over with a new quotation: no need to repaint...easy peasy!
First you cut out your letters. I like to use batik fabrics because the weave is nice and tight. I also cut my letters freehand; I don't mind the imperfections. If you're not up to that, you could stencil letters to the shiny side of freezer paper using a nice dark pen (like a Sharpie). Iron the shiny side onto the back of your fabric, cut out the letters (the pen should show through enough for cutting), then peel off the freezer paper. The freezer paper also keeps the fabric stiff for cutting, but watch when you're peeling so you don't get too many frayed ends.
Press your letter against your (clean) wall. I like to do one word at a time, stand back & make sure it looks straight/even, and peel the letters off if necessary. You can reapply them without adding more starch if you do it quickly.