GB/GBC/GBA: VisualBoyAdvance
NES: FCE Ultra (best I've encountered for Windows)
SNES: ZSNES (ipher's wip builds) sucks ass they took out NetPlay

N64: Project64 works beautifully with the 6 good games for that system o_O
PSX: ePSXe (great with all the games I have except Chrono Trigger)

PS2: PCSX2 (very experimental, but the next release will allow FFX and X-2 to be played without graphic corruption, still runs 60+FPS on my system)
I'd like to try a recent build of a Gamecube emulator. I don't have any ISOs for that system anymore. Super Mario Sunshine ran like ass on my Athlon 3200+ a couple years ago. :/
Jam it back in, in the dark.