Cone
Piezo
Horn
Dome
Linaeum™
Planar
Quasi-Ribbon
Ribbon
Electrostatic
Bending Wave Transducer (AKA Manger)
Plasma
Corona (similar to Plasma)
(plus others I'm sure......)
Of all these the Plasma and Corona most accuratly depict natural sound, however they are by far the most impractical and dangerous of the bunch. The Manger is very well regarded, but its more of a full range unit. The electrostatic and ribbon are probably the best as far price/performance, but have size requirements. The planar tweeters such as Dayton, Hi-Vi, and Bohlender Graebener ones are more affordable, and better sized. Domes are great because they are small, pretty damn good, affordable, and proven. Horns have great sensitivity and an occult following. Cones usually have pretty good frequency response due to more excusion, however most cone "tweeters" are cheap garbage, and you have to look at the "full" or "extended" range drivers to find the real gems.