My sketchbook studies come from a wide variety of times and places both local and abroad. I like to keep them small (roughly 3"x 5") and quick (30 minutes give or take), I paint with watercolors and gouache (materials list for you in the sidebar). Enjoy!
If you'll allow an occasional digital sketch thrown in with the usual watercolor and gouache pieces, this is done in Art Rage and Photoshop. It did begin as an on location gouache sketch but I ended up messing around with it digitally.