Infinity Monitor Jr from 1976. Peerless KO10DT tweeter, German Peerless 2" soft dome mid, 12" woofer. Enough baffle step compensation to be able to be placed away from walls on a stand. Least expensive speaker that did imaging right in its day, and the inspiration for a lot of my DIY work (although I stayed away from the first order crossovers). I'll speculate that the directivity mismatch at 600 Hz is less audible than in typical two-ways. OK, I liked the Infinity IRS better, but who wouldn't?
Other favorites: Apogee Duetta, Eminent Technology LFT8, Duntech Sovereign.