Nice little site that lists hundreds of common language errors, including some lesser-known common mistakes. It also aims to confirm usages that the pedants are normally ‘correcting’:
Till vs ’til
Since it looks like an abbreviation for “until,†some people argue that this word should always be spelled “’til†(though not all insist on the apostrophe). However, “till†has regularly occurred as a spelling of this word for over 800 years and it’s actually older than “until.†It is perfectly good English.