This right here is my "Masters of Doom" inspired attempt at a canvas-based Javascript raycaster. It works at 640x480 @ 60 FPS, and features texture walls, ceiling and floors. The floors and ceilings can have different levels (like the original Doom). I'm done with it for now, but if you want to hack at it, feel free to fork :).
If you want to play with it locally, don't run it from the filesystem - your browser will complain about security. You'll have to set up an HTTP server to serve this.