I've been developing this project for some time now, and now the project is getting so big I can't do it alone. It's called Octoduino. Basically the idea of the project is that (at some point), you will be able to program the Arduino using any programming language and loading programs from an SD card.
Now you may be also wondering, how the heck is that going to fit on an Arduino? Well, it already doesn't fit on some of the smaller Arduinos like the Due (Edit: Duemilanova). Octoduino utilizes a SWAP-style memory storage system on the SD card, so the JS/Java/Whatever program doesn't eat up memory.
Right now the project is still in it's early stages, there's still some unstable stuff, no real languages are supported yet, but community involvement is really helpful.
Correction: One language is supported, ParseBasic. It's a custom interpreted language I'm developing for the purpose of writing interpreters for other languages.
If you're interested, the project is hosted at GitHub - NETponents/octoduino: Arduino sketch that allows programming in multiple scripting languages from an SD card.. If you need communication faster than here or GitHub issues, we have a gitter.im room (use your GitHub account to log in). To join, click the badge in README.md.
Thanks!