Here is a hypothesis of relationshp which I believe to be quite robust, although it too is subject to revision as evidence from better characters can be found.
The diagram depicted below was published in the article:
Philip J. Heise, Linda R. Maxson, Herndon G. Dowling, and S. Blair Hedges 1995. Higher-Level Snake Phylogeny Inferred from Mitochondrial DNA Sequences of 12s rRNA and 16s rRNA Genes. Mol. Biol. Evol. 12(2):259-265.



