Lots of components, very few regrets.
Here are the ones that I definitely regret selling, though I doubt I will ever re-buy them:
Musical Fidelity Nu-Vista 3D CD player
Marantz 8b (VAC reissue from the 90s)
Gryphon Diablo integrated amp (regret was losing the internal phono stage)
Here are the items that I have sold...and then gone back and re-bought after determining that I was an idiot for selling:
Naim NACA5 speaker cable
Dynaco ST-70
Here are the items that I have sold, and the jury is still out on whether I may buy them again:
JBL L300 Summits
Naim ARO tonearm
There are a lot of components that I dont have any regrets selling, but I did have the utmost respect for these components when we parted ways and was very sad to see them go:
EAR 861 amplifier
Sonus Faber Electa Amator II