With the thread about Commodore Emu, which I'm pretty knowledgeable about, I thought I'd grab a few significant project links for the Atari Crowd.
(I once had a first gen Atari 400 with the Chiclet Keyboard I rescued from the trash with a cut RF cord, and in hind sight, I wish I had held onto it and tried to get some peripherals. I patched the RF cord and came up with a handful of cartridges, and since the Atari uses the same game controllers as my Commodores, I had plenty to play it. I had fun with it for a few months and sold it on Fidonet for $35 - Yes, it was a long time ago.)
I had one friend at that time who had a newer 800 with only two joystick ports. He had one game that wasn't really playable on his because it was meant for 4 players with 4 joysticks. He never got to try it before my 400 came along.
Anyways, want to support that community too.
Here some links
http://www.atarimax.com/ - A method to make a hard drive solution for your Atari. There are some options for ColecoVision too!
http://ftp.pigwa.net/stuff/collections/nir_dary_cds/Games/FILES/ Massive FTP site full of Atari Games and Utilities
http://www.atari.org/ The base for a large Atari Web Ring - All kinds of places related to Atari you can go to from here! Emulators, software sites, and much more.