QuikQuak Upstereo is a free stereo enhancer plugin effect for Windows and Mac.

Description:

UpStereo is a simple, useful tool – it makes your mixes bigger, in stereo width and loudness.
Using three basic basic systems:

• A fixed frequency EQ designed to lift the highest audio frequencies, and boost the bass.
• A stereo width unit, for expanding stereo sounds so they appear wider and fatter. At extreme levels other characteristics are also brought out of the sound, so this can also be used as a tonal control for individual instruments. This also has a mono setting, useful for squashing up those aggressive samples that take over the mix.
• A loudness button that raises the waveform to the limits in a smooth curve. This saturation gives the mix a more perceived loudness, without clipping.

These stages create an overall loudness effect on the final output, so a gain control is included to keep the limits in check.