Illustrator:

Tutorial: http://vectips.com/tutorials/create-sketchy-style-vectors/

Tutorial: http://www.blog.spoongraphics.co.uk/tutorials/how-to-create-a-cute-vector-mushroom-character

Tutorial: http://www.blog.spoongraphics.co.uk/tutorials/create-a-cute-vector-penguin-character-in-illustrator

Tutorial: http://www.blog.spoongraphics.co.uk/tutorials/how-to-create-a-grumpy-troll-character-in-illustrator