Triptyque is a free Max for Live synthesizer aimed at creating special effects.
MiniSpillage is a free professional quality drum synthesizer plugin featuring high resolution 64-bit DSP processing.
WaveDuo is a monophonic/paraphonic wavetable synthesizer by Jonathan Tremblay. Available to buy and in the NI Reaktor User Library.
Music Radar deconstruct this powerful freeware synthesizer and show you how to build a patch from the ground up.