Pioneer SX-1050
I had given my friend a great deal on two pairs of Cerwin-Vega D-9's. The combined load from running both pairs however wasn't being handled well by the little Yamaha HT receiver he was using. So I "sold" him the SX-1050 I had for basically no money, with the idea that he was going to give it back to me once he got a more powerful unit of his own.
The SX-1050 itself was a unit I picked up for $10 at the local flea market ~12 years ago. It had something broken in the preamp section but the amp section worked great. My friend uses his Yamaha receiver as a preamp and the Pioneer receiver as an amp. Well... a decade later and my friend is still using the exact same setup, and hasn't given the SX-1050 back. Not sure if I "regret" giving it to him or not, since he has certainly got a lot of use out of it, but just the same, I'd love to have it back and get that thing restored back to it's original beauty.