Aegilops, eight letters long, is the longest word whose letters are arranged in alphabetical order. Seven letter words with this property include beefily and billowy. Six letter words include abhors, accent, access, almost, biopsy, bijoux, billow, chintz, effort, and ghosty.
Go on,quizmonkey, satisfy my curiosity, what or who is an aegilops [and where on earth did you find it?] Even the famous Mr Ben Schott hasn't come up with that one!!