More than forty thousand words, including newer scientific and technological terms, are compiled in a spelling guide, along with guidelines for using compound words, the rules for forming plurals, and the seven basic rules of spelling.
Kind of embarrassing to admit, but I probably use this little book twice a week. It's very user friendly and does seem to contain just about every word I habitually misspell. Its only flaw is that I think it could be a bit longer, but I guess that would interfere with how convenient it is to use.