WinUAE - Official Site
Download Verison 2.3.1 (3.0MB)
I must confess that I have not used this Amiga emulator myself, but everyone says that it is the best around (for Windows), and it is still regularly updated.
(Last Updated: February 26, 2011)
 Atari 2600
Download Verison 2.6 (1.57MB)
Atari 2600 was a classic system, and everyone tells me that this version is one of the best emulators (for Windows).
(Last Updated: March 2002)
 BBC Micro / Master 128
BeebEm - Official Site
Download Version 4.13 (4.0 MB)

This is a BBC Micro and Master 128 emulator. If you're like me, you have never heard of these systems before. That's okay, they're still fun.
(Last Updated: January 22, 2011)
Download Version 1.31 (624k)
This is a ColecoVision emulator. I never used one myself, but the 49 games included in this zip file are bound to be worth at least a few hours exploration.
(Last Updated: April 28, 2002)
 Commodore 64
CCS64 - Official Site
Download Version 3.8 (2.0MB)

This is an emulator for the old Commodore 64 computer system. Many other abandonware sites offer games that go with this, so you should have little trouble finding something to play.
(Last Updated: March 20, 2010)
 Gameboy / Gameboy Color / Gameboy Advance
VisualBoy Advance - Official Site
Download Version 1.7.2 (597k)
Download Version 1.7.2 (588k)
I used to mess around with a number of poor quality gameboy emulators, and then I found this and never used another again. It runs all Gameboy, Gameboy Color, and GBA.
(Last Updated: May 25, 2004)
 MS-DOS (MicroSoft Disk Operating System)
DOSBox - Official Site
Download Version 0.7.4 (1.2 MB)
Download Version 0.7.4 (2.9MB)

DOSBox is a must-have for classic DOS gaming. It has very high compatibility for old games that do not run well on newer versions of Windows. There is also a version for OS X as well, which is good for me because I don't use my PC these days.
(Last Updated: May 12, 2010)
 Nintendo 64
This is a highly stable and compatible Nintendo 64 emulator for Windows. Some N64 Games are difficult to play on a computer, but its the idea that counts.
This is the most current Nintendo 64 emulator for OS X, with a few updates each year. Without an appropriate controller N64 emulation is a bit difficult.
(Last Updated: April 10, 2010)
 NES (Nintendo Entertainment System)
This isn't the best NES emulator anymore, but it was the main NES emulator for years without any problems, and it is very user friendly. This verison is for DOS and Windows 95+.
(Last Updated: September 22, 1997)
Nestopia - Official Windows Site - Official Mac Site
Download Version 1.4.0 (989k)
Download Version 1.4.1 (2.2MB)
This is the best NES emulator for Windows or OS X. It includes controller support (including the lightgun), online netplay, and support for the Famicom Disk System.
(Last Updated: June 11, 2008)
 Playstation 1 (PS1/PSX/PSOne)
PCSX - Official Windows Site - Official Mac Site
Download Version 1.5 (168K)
Download Version 1.5 (1.2MB)

This emulator works well for running Playstation 1 games. As with other emulators for more advanced consoles, you will have to find the BIOS files yourself.
(Last Updated: September 17, 2003)
 Playstation 2 (PS2)
PCSX2 - Official Site
Download Version 0.9.6 (2.5MB)
Download OS X 10.5 Version (6.4MB)
Download OS X 10.6.3 Version (6.1MB)

As far as I know this is about as close as you can get to playing PS2 games on your PC. Once again, you will need to find the BIOS files on your own, or just figure out how to copy them from your own PS2. Good luck!
(Last Updated: March 3, 2009)
 ScummVM (Lucas Arts Adventures)
ScummVM - Official Site
Download Version 1.2.1 (5.5MB)
Download Version 1.2.1 (10.3MB)

The Scumm Virtual Machine (ScummVM) is a program that will run (flawlessly it seems) games such as Simon the Sorcer, Beneath a Steel Sky, Day of the Tentacle, Flight of the Amazon Queen, and other LucasArts games.
(Last Updated: December 19, 2010)
 SEGA Genesis / Master System / 32x / CD
SMS Plus - Official Windows Site - Official Mac Site
Download Version 1.3 (1.3MB)
Download Version 1.3 (1.3MB)
Download Version 1.3.3 (1.3MB)

SMS Plus is the most compatible emulator available for Sega Master System and Game Gear, and is available on many more platforms if you visit the official site.
(Last Updated: September 27, 2008)
Genesis Plus - Official Windows Site - Official Mac Site
Download Version 1.2a (460k)
Download Version 1.2a (192k)
Download Version 1.3.1 (1.3MB)

Genesis Plus is the most compatible emulator available for Sega Genesis and Mega Drive, and is available on many more platforms if you visit the official site.
(Last Updated: January 16, 2010)
Genecyst - Official Site
Download Version 0.32+ (423k)

This Genesis emulator for DOS is almost exactly like the NES emulator Nesticle. It doesn't feel as clean as Gens, but still runs most games just fine.
(Last Updated: August 18, 1998)
 Sinclair ZX Spectrum
Spec 256 - Official Site
Download Version 1.2 (108k)

This is a Sinclair ZX Spectrum emulator. It runs pretty much like the old Spectrum system, but without the long load times. I have not included any games, but for old fans of this system, this is where to start.
(Last Updated: 1999)
 SNES (Super Nintendo Entertainment System)
ZSNES - Official Site
Download Version 1.51 (848k)
This is the best Super Nintendo emulator available, at least among those that I have tried. It has great compatibility, sound, gameplay...and so much more. That, and it's for one of the best consoles ever.
(Last Updated: January 4, 2007)
 TI-99 (Texas Instruments 99)
Classic99 - Official Site
Download Version 0.346 (2.8MB)

This is an emulator for the TI-99 home computer. If any of you are old enough to have used one of these, well, weren't they great? This zip file includes many of the old classic games as well, enjoy!
(Last Updated: February 17, 2011)