AtariAge Just about everything you every wanted to know about the Atari 2600 can be found here
Atari Mania A comprehensive database/collection of all things Atari-related, including ROMs, snapshots and instructions, user guides, and more
Atari 2600 on Wikipedia Historical information about the Atari 2600 console
Stella on Wikipedia Wikipedia page for Stella itself
 
Stelladaptor

2600-daptor

Bliss-Box