Agreed, MAME is definitely one to get. You will have masses of original arcade games in your pocket thenYes neogeo is a must have and I would add mame in there too. There is so many to pick from and your SD card becomes small so fast. It is hard to name them all. But, yes, they are all good.
Yes, the Genesis and Megadrive are both a must...I don't want to sound like an dick, but all of them. The genisis is a must, the nintendo is a must, the megadrive is a must, the neogeo is a must, etc. All of them.
My favorites are, gp2xhandy (lynx), Gp2xspectrum (speccy), Vice (commodore machines), MAME, Neo Geo, gnuboy (gameboy/colour), Castaway (atari st), uae4all (amiga), alexkidd (sms & GG), PC Engine (hu), nes (gpfce) and ofcourse megadrive and snes
Yes, the Genesis and Megadrive are both a must...
Caprice for Amstrad CPC.