stereo effects

What are the best (preferably standalone) digital effect units for experimenting and listening with different "sounds" (tube or "analog" sound) on your otherwise transparent hi-fi system (where the audio comes from digital sources) ? Would you use some stereo guitar effect/multi-effect units or...

Post titles (your favourite or "just" quality/reference grade) that feature some clear "stereo" separation/effects. Any genre, era.. If possible, try to insert media in your posts. Hope I start with nice examples :) Keith Richards - Hate It When You Leave Eagles - One Of These Nights