These are links to the most commonly used online resources when conducting word investigations. We also keep our classroom reference shelf stocked with word-origin/definition type books.
At Word Works there are great videos to watch, as well as links to current Real Spelling moments in classrooms around the world.
At Real Spelling there are informative videos on a number of spelling/morphology/etymology/phonology topics.
Real Spellers is a place where people post their questions about spellings, and where others can reply. There is lots of great information here.