I use a jailbroken Nintendo Wii with the homebrew channel installed on it. It has 32 GB SD card full of NES, SNES, Sega Genesis, Sega CD, and PC Engine games. I also connected a 40 GB hard drive via USB full of Gamecube games. It's really convenient, since most of these support Wii remotes, Wii classic controller, and Gamecube controllers.
N64 and Playstation emulators for the Wii are available as well, they just weren't as big of a priority for me so I haven't checked how well they perform.
N64 is spotty at best, PSX is actually decent. Despite that, I second softmodded wii. It takes about thirty minutes to do, there are tons of great games that work well on it, and Wiis pop up for very cheap (I have bought two this year for $10 each)
Other than that, a cheap PC. Refurb business laptops popup for $100ish on Ebay, they will run everything up to 6th gen - sans Saturn.