Reference 3A Dulcet
Reference 3A deCapo
Zu Tone
These speakers give you tweeters and therefore full harmonic representation of what's going on. Omegas are interesting but aren't wideband enough, IMO, to qualify as monitors. These three speakers will also give you decent bass.
Another borderline efficiency contender that is excellent, is the Silverline SR17-II. The Zu uses a full-range driver from 50Hz - 12kHz, with the tweeter rolled in on a high-pass filter above 12kHz. The Ref 3As have a similar topology, but the tweeter rolls in much lower, in midrange territory like most 2-ways.
Phil