Here is a list of emulator that I have on my Cab or that i have tried.
** 
Arcade **
=> Mame
=> Model 2 Emulator :  Most sega model 2 games run slow in mame
=> Zinc : For playstation based games - most of them run well in mame with a decent config
=> BlazBlue CS : the taito X2 game - that is not really an emulator
** 
 Naomi(arcade) ** 
Naomi is the arcade equivalent of the dreamcast.
=> Makaron : Best emulator but requires a good computer. A little complicated to configure.
=> Demul : Faster than Makaron. Run also Atomiswave Games (kof neofighters, etc.). Can play vertical shoot'em up on an horizontal screen (ikaruga, etc.).
=> NullDC : Faster than Demul, but the second player doesn't work for naomi games.
** 
 Dreamcast ** 
=> NullDC
=> Makaron
=> Demul
** 
 Nintendo 64**
=> Project64
** 
 PS2 **
=> PCSX2 : Requires a very good computer and can play a lot of the games. I used it for Metal Slug 6, but now you can find a PC version.
** 
 GameCube and Wii **
=> Dolphin : Requires a very good computer (64bits is a lot faster) and can play a lot games. I tested new super mario bros wii successfully at full speed.
** 
 Nintendo DS/GBA **
=> No$gba 2.6a : Requires a good computer for DS games. I was not able to run super mario DS full speed.
=> Desmume : Requires a good computer too.
** 
 Genesis/Sega CD/... **
=> Kega Fusion
** 
 SNES **
=> Zsnes
** 
 Playstation **
=> ePSXe
There is more emulators like psp (Jpcsp), Virtual Boy (vbjin,Mednafen, etc.) but i haven't try them. If you start with those, it should keep you busy for a while 
