I have used DICOPT using the NEOS server (http://www.neos-server.org/neos/solvers/minco:DICOPT/GAMS.html) to solve large (approx 1k variables and 1k constraints) mixed integer non-linear programs and found it excellent.
For my problem DICOPT did much better than the other MINLP solvers listed on the neos server BARON/KNITRO/LINDO/SBB etc.
There are certain constraints to submitting jobs to NEOS and it is slightly cumbersome but the free access to a powerful commercial solver more than makes up for it.
