StereoFX is a universal binary AU plugin and one of the best stereo widener plugs out there. It is a stereo expander so center images remain stable, and it widens far-field information like reverb better than anything. Now with mid-squash. Mono-friendly. StereoFX is $59.99.
Be aware, though, that it's not designed to change the stereo image radically- this is a mastering-style widener at its best when adjusting stereo subtly. If you push it very hard, stereo content will develop a distorted quality, so don't try to use it in place of mixing adjustments. StereoFX is for widening (or bass mono-ing) meant not to be obvious.
Try the demo of this by downloading the demo collection! You're not allowed to use the demo for actual work. It politely mutes itself briefly every couple minutes, and that's the only thing it does to spite you. It won't expire or do anything to you, and when you get the actual plugin, throw away the demo and put the real version in its place and most software should replace saved instances of the demo with the real thing seamlessly, retaining any settings. Please support my cooperative, unhostile demos with sales of the real software.
