Even though I've had a page devoted to Graffiti on this site, I added this one for Lettering after stumbling across Christopher Rouleau's Sign Painting site as well as this worksheet from Amy Peppler Adams' site, which she offers (for free), this downloadable worksheet "The Alphabet 100 Project," which is a year-long worksheet to draw 100 variations of a letter of the alphabet.
Very Cool Lettering Sites (imho)
GraphicDesignJunction.com, is a collection of remarkable typography artwork inspiration designs, lettering quotesand calligraphy illustrated artwork by professional graphics designers. In this showcase, we’ve put together a list of thirty four lettering and illustrated typography designs.
LingoJam.com/CoolTextFonts is a wild site: it lets you type characters in a variety of fonts that aren't on your system, then paste them into other graphic sites like Canva.com and somehow codes the font algorythms into the layout.