Lua

So what do you think of Lua?
I'm considering it for my X3 inspired(cloned) game as a scripting language for all the entities, and co-routines emulate the "@" operator of X3 scripting language perfectly.
I just hope I can integrate it to my code without much trouble.

About as fast a scripting language as you can cram in for real-time 3D.  I was using it for Quake 2 scripting extensions with stuff that ran on a per-frame basis (I forgot how many frames per second servers run at...) and it did fine.  Closures make for great event handling mechanisms.

The only problem I ever had with Lua is that there's no stable threading implementation... you sort of have to hope you don't screw up.  A runner-up for me is Ruby, but it's going to be significantly slower (but a lot nicer to code in).