I like to collect little bottles for my vases, but I never pay more than $3 for them. I was surprised by watching Travel Channel's Cash & Treasures how popular and expensive those little glass bottles can be. Beautiful but so expensive.
Dating your bitters bottles.
Recognizing Historical Sites and Artifacts, dating bottles.
Australian Bottle & Collectibles.
Expensive perfume bottles (with the perfume).
Utah bottle collectors.
Antique Bottle Shows
Added later: Found Jeff Crandall wonderful Poet's Bottles via Daily Poetics and realized it must be an addition to this entry!