Here is an article (by Terence Parr, the author of antlr) about LL(*) grammar analysis: articlearticle with a nice example of what is LL(*) but not LL(k), for any k.
Another good reference (and much more complete) is the "Definitive ANTLR Reference", again by Terence Parr, and the original journal article describing how antlr works [pdf].