Super Mario Brothers (including all glitches and bugs in the original game) got ported or emulated to the Nintendo Advanced (older and probably difficult to get) and is available via the Wii's Virtual Console. (I never managed to rescue the princess). I'm sure there are also unlicensed versions and ROMs for the PC around.
Versions of Tetris or Tetris-like games are available for virtually every system you can imagine, including the iPod and other mobile devices.
As far as I see, QBert is currently only available as a ROM to be played via the MAME emulator (unless you want to hunt down the SNES version).
