I quite like the approach taken in MetaLua (http://metalua.luaforge.net/) for allowing more advanced cases of meta-level programming. After some exposure, moving up and down levels using +{} and -{} becomes about as readable as meta-programming can IMHO. The explicit modification of the compiler is not so nice, but I'm guessing it is hard to do anything better in a a programming language with some actual syntax.

Of course, what I really would like to use is MetaLuaJIT, to get the best of all worlds :)