MAME Wii is an Arcade Emulator based on SDLMAME. Many games for early arcade boards can be played with varying amounts of success.

Issues
Lots of ROMs are supported, but not all of them. If you don't see the ROM in the list in the emulator, then support for that ROM isn't included. This is to keep the size of the emulator low enough to run effectively on the Wii. A list of all the ones that are can be found here: http://www.toadking.com/wiimame-0.4.txt
Just because a ROM is supported does not mean it will run. Even games for early boards like CPS-1 can fail to run due to RAM limitations. If the emulator suddenly kicks you out to the Homebrew Channel, look in the MAME folder (sd:/mame/) for a file called errors.txt. If it says something about failing to allocate space, then odds are the ROM can't run on the Wii. The emulator might also crash outright and leave you with a code dump if RAM runs out.
Because the Wii is not a strong console, some games will be slow. Frameskipping is enabled by default to make games playable.
On older TVs, the edges of the screen can be cut off. To fix this, in mame.ini, look for the option "safearea" and set the value to something around 0.8 and 0.95. It will vary depending on your TV.
Changelog
1.0 - December 13, 2011
Rewritten frontend code entirely, no longer uses SDL.
Added better joystick support; Gamecube joystick works!

http://wiibrew.org/wiki/MAME_Wii