This licentiate thesis gives a nice summary of most available tools and their pros and cons: http://www.csc.kth.se/~xmartin/papers/licthesis_xmartin_notrims.pdf
These papers might be useful as well: http://www.mitpressjournals.org/doi/abs/10.1162/COLI_a_00123#.U8U-2fl_uSo