Two recent spottings highlight a fun new business idea that will definitely appeal to consumers' gravanity: personalized avatars in their own image. Based in Brooklyn, graphic artist Lina Chen creates digitally illustrated portraits. Working from photographs, her black and white images are stylized likenesses of their subjects. The finished product is a digital file, delivered as a vector image, which lets customers enlarge their portrait without losing image quality. In a small size, digi-portraits make excellent avatars or buddy icons. Prices depend on a portrait's complexity. Meanwhile, in Britain, Cute Little Blokes is targeting gay consumers who'd like a caricature…