I just bought Activision Anthology for the GameBoy Advance. It include 55 Atari 2600 games including selections published by Activision plus some demo titles and games written long after the 2600 had left the scene.
It is especially nice that the Activision titles are the focus here. Activision was one of the most innovative 2600 developers. They made the 2600 hardware do things that is was not supposed to be able to do. The games are in general, a notch above the others.
The cart runs the well known Stella 2600 emulator. I know this because Bradford Mott is the lead emulator developer for the cart and he wrote Stella.
It completely rocks. Enduro, Spider Fighter, Megamania, Chopper Command, Air Raid, Pitfall...all the great ones are there.
It saves best scores, and rewards you with cheats that change the games. Scans of the cart label, box art and instructions are included in the game. A steal for $29.