I am not easily impressed by web sites because normally they are glitzy and shallow, or worse, shallow and ugly. I just hate the ugly ones.
Shmoop is worth checking out, though. It covers Literature, US History and Poetry right now with more coming, complete with headings like, "In a Nutshell" and "Why Should I Care?" Any website that includes Bob Dylan's "All Along the Watchtower" in their Poetry section and proceeds to discuss it in an engaging, intelligent way makes me sit up and take notice.