GBA
Why would anybody want to play handheld games on a computer?? Two words: TEST DRIVE!!  If anybody from Nintendo is reading this, then POO!! on you. I bought a Gameboy Advance during Christmas the year it came out, simply based on games that I had previously tried on Visual Boy Advance. Before that, I wasn't so sure about owning another handheld, but after trying Super Mario Advance, Mario Kart Super Circuit, and Gradius Galaxies, I went out and bought them all.

For most of your Gameboy needs, Visual Boy Advance does it all; Gameboy, Super GB, GB Color, and GB Advance.

However, one emulator I never see mentioned anywhere is HeboWin. I'm guessing that's because it's in Japanese, and it was hosted on a bare Geocities page, which is now dead. One thing that was built into the Gameboy Color was a built-in palette for full color support for some of the original GB games, such as Tetris, Donkey Kong, Super Mario Land series, Metroid II, etc. Hebowin is the only emulator I know of that supports this. I remember reading this once on a news site (can't remember which one), and that was the last I ever saw of it. Go around and try to find Hebowin mentioned anywhere or how to run it on any other major emulation site; I bet you can't and it's a shame, because the older games look really good with the new colors.

So now, for the first time on an English emulation site, here's how to run Hebowin:

Metroid II Donkey Kong Super Mario Land 2 Pokemon Yellow Super Mario Advance 2 Gradius Galaxies