Merriam-Webster's Collegiate Dictionary: Provides both sound-alike and spelled-similarly alternatives for queries that retrieve no hits. Part of the Britannica Online service.
Oxford Reference Online: Oxford Reference Online brings together language and subject reference works from one of the world's biggest reference publishers into a single cross-searchable resource.
Xreferplus: xreferplus includes encyclopedias, dictionaries, thesauri, and books of quotations, not to mention a range of subject-specific titles covering everything from art to accountancy, and literature to law.
