Neowin reports Paul Holden has created a JavaScript-based N64 emulator. The emulator requires WebGL (which isn't supported by IE), and it's more proof-of-concept than usable because it's very slow.
After what was probably a lot of late nights and empty cans of Red Bull, Holden has the project in a working manner. He admits it is still limited, but that it works for a small number of games. Super Mario 64 plays, and a number of other games do, but he warns they may display graphical glitches.
If you'd like to give Holden's N64 emulator a go, try it here. You need your own ROMs, and either Chrome or a Firefox Nightly build. Older versions of Firefox do not have the same features needed to use the emulator, which he feels will still take time to become usable. Now you can either relive old classics, or try out the competition's games.
