http://www.uv.es/ruizcan/p_vst.htm
http://www.voxengo.com/group/freevst/
Baxxpander is a bass enhancer
Xcita is a harmonic exciter
Stereo Touch is a stereo enhancer
and
StereoTool by Flux is on my page and is a great stereo imager.
But remember I don't recommend using any of these (except Flux Stereo Tool) because you should fix the problems before these tools are needed. Bass enhancer doesn't mean drop this plug on every bass and kick for a great hard hitting bass sound. It means use this only when your bass is lacking, but 99 times out of 100 the only thing lacking in the bass is the ability to hear it through crappy monitors. And usually better mixes have the bass turned down lower than you would like.