Atari 2600

Acorn Virtual 2600
Emulator port for Acorn RISC OS.
http://www.mnementh.co.uk/v2600/

Atari VCS Preservation Retrogaming Archive
514 ROM Images in one zip file. [Requires Flash]
http://atarigamer.tripod.com/

AtariAge: 2600 Emulation
Resources and links to the most popular emulators and utilities.
http://www.atariage.com/2600/emulation/

GP32 Atari 2600 Emulator
Port of Virtual VCS emulator to the GP32.
http://www.atariage.com/2600/emulation/GP32/

Imdylanks Atari Roms
A collection of ROM Images packed in three files.
http://www.geocities.com/imdylank/user.html

JStella
Java-based emulator that works as an applet or as a stand-alone program.
http://jstella.sourceforge.net/

Paul Robson's A26
DOS based open source emulator.
http://members.aol.com/autismuk/emu.html

Stella
An open source emulator for DOS, GP2X, Linux, MacOS, Unix, Windows, and Windows CE.
http://stella.sourceforge.net/

StellaX
Windows 9x, NT and 2000 port of Stella.
http://www.emuunlim.com/stellax/

Virtual 2600
Historical look at Alex Hornby's Virtual 2600 emulator. Virtual 2600 is an open source emulator for DOS and Unix.
http://www.hornby.dsl.pipex.com/v2600/

z26
An open source emulator for DOS, Linux, and Windows based on Paul Robson's A26.
http://www.whimsey.com/z26/