This forum is flooded with spelling mistakes. Continuing on the effort of promoting better communication skills (as recent "Learn to Spell" thread suggested), here are the two links that can give you a great start.
Is "advertizing" a spelling mistake or a localized spelling? It's got 140,000 entries at Google and is listed in some smaller dictionaries, but not Webster's, American Heritage or any of the major dictionaries.
Variants are words that are WRONG but put in the Dictionary because people use them. Some of those words might be included. If it's listed as a "variant" or something, it's likely to actually be wrong.
By the way, language is constantly evolving. If there is a good reason for a spelling change and it catches on with the masses, it could very well become official. That's how language was created and how it develops to become more effective for communication.