I'd like to point out the website of a new arcade emulator called JEmu2. Well, it's not entirely new but it never had an official website before and has been offline for a long time.
* The easiest way to experience arcade emulation by a one-click install and automatic updating (it's deployed through Java Web Start).
* OpenGL rendering
* Online high score saving (currently just for 3 games, but more games will support this)
* Sound (although not all games support sound)
* Runs on Windows, Linux and Mac OSX
* Currently, 28 games are supported (more to follow)
You will need java 1.4 or higher installed and OpenGL.
You can find JEmu2 at http://www.gagaplay.com