VST Stereo Expansion
 

What's the best stereo expander money can buy? (If it's free that's cool too) But let's say I have unlimited funds, what would be the BEST stereo expander out there?

Do you mean upward compressor/expander or stereo imaging?

More along the lines of imaging.
Sometimes they're called "Stereo Enhancers"

Gotcha.
Well, WAVES is an industry standard for VST plugs and their mastering bundles have a stereo imager. I have the Gold bundle and it includes it, but all their packages are preeeetty expensive, but obviously very very good. I won't tell you that it's definitely available on torrents for free.... Nor will I tell you that if you do a Google search right now, you'll be sitting on a bundle of that and lots of other fantastic plugs for free in under 5 minutes...... but I will tell you it's worth it to at least look up what WAVES has to offer.

You should also be aware of the site KVR: Virtual Instruments, Virtual Effects, VST Plugins, Audio Units (AU), DirectX (DX), Universal Binary Compatibility - Audio Plugin News, Reviews and Community, which is a site cataloging and providing downloads of thousands of searchable VST and VSTi plugins of every variety, including imagers, both free and demos. You'd be surprised at the quality of free VST plugs, and once you try a couple out, you may no longer find yourself in the market for the most expensive thing out there.
With software plugins, your quality is going to come from the algorithms and programming of the plug itself. The features are going to be pretty standard across the board, so really your best bet is to try as many free downloads as you can and settle for the imager that doesn't color your sound, doesn't degrade it in any way, and provides the features and usability you require.

Another thing to remember is a stereo imager/enhancer can only do so much. If you're trying to widen your stereo field but your mixing isn't proper (I.E. frequency mush, poor panning practices, etc..) then you're going to get limited results regardless of how good your stereo imager is. If your mixing is on par, then a standard imager that doesn't color your sound is all you'll need... and that's definitely available free.

Think it over and give yourself some time to consider the possibilities before you spring out and pay for something you may not need.

GL.