The Chelsea logo was originally a simple "CFC" and (embarrassingly for some) one of an old pensioner. This was changed in the 1950s by Ted Drake who wanted to modernise the club's image. Soon the club used the now famous image of the lion holding a staff which is the Earl of Cadogan's coat of arms.
The official club badge at the time contained a blue lion rampant holding a golden crozier against a white background. The lion is derived from the arms of Earl Cadogan. The crozier was that of the Abbot of Westminster whose jurisdiction extended over Chelsea. Three roses and two footballs in gold encircle the top of the badge.
In the mid 1980s Le Coq Sportif decided to change the crest to a lion sitting on top of CFC lettering which was not popular with Chelsea fans, as it looked too similar to Millwall's crest.
Finally in 2005 Chelsea reverted to the old lion crest, with some amendments as the club was not willing to pay the Earl of Cadogan for the rights to use the old badge. The majority of Chelsea fans prefer this new badge to the "CFC" one from the 80s, but all would prefer a return to the old Chelsea lion. See the Official Chelsea site for a better reference.
Individual pin badges collected & uploaded to date: