Download Spitfish De-Esser:

De-esser plugin for vocals

The free Spitfish de-esser VST plugin by Digital Fish Phones is an easy to use de-esser effect, aimed mainly at vocal tracks (mono or stereo). Just like the classic analog hardware de-essers, the Spitfish de-esser dynamically filters out harsh, annoying s-like sounds that would otherwise 'spit' in your face.
The Spitfish de-esser can be used both for taking out the harsh consonants and sibilance of a vocal track, as well as for taming other unwanted frequencies (e.g. from cymbals) in your mixes. Windows 32-bits only.