(from https://photo.stackexchange.com/questions/496/what-do-all-those-cryptic-number-and-letter-codes-in-a-lens-name-mean)
Brand Lenses
Most major camera manufacturers offer their own line of lenses. Such lenses tend to follow the most stringent quality guidelines, and often come with a price premium.
UPDATE: Sony lens format abbreviations
Off-Brand Lenses
Most off-brand lens manufacturers make lenses that fit many types of bodies, including Canon, Nikon, etc.
Descriptions by Lens Features
If you know what feature you’re looking for in a lens (cropped-frame designation ultrasonic motor, low-dispersion elements, image stabilization, etc.), and want to know what each of the brands call that feature, the following answers are organized by lens feature.
Lens Database
Comprehensive database of most major brands.