Aside form the Human voice...

T-bone brings up an important question. What expressive techniques do musicians have available on different instruments? Earlier in the thread frequency range was sighted. In addition there is dynamic range, tonal & timbre range, articulation, pitch control/vibrato, and phrasing. All these things contribute to the possibilities of expressive control by the artist. Different instruments have different amounts and ways of applying these techniques. For example, prepared piano, or plucking, damping, striking the strings with implements, expands the expressive range of the piano. Mutes expand the range of brass instruments. Bowing techniques add expressive range to strings and tonguing techniques to winds. Add breath control, electronic and computer manipulations, different stops for the organ, double stops, triple stops, polyphonics, subharmonics, overtones, plus an array of other experimental techniques and there opens up a plethora of potential. Even if we disregard all the 'artificial' means, there's still the subtle, elusive, yet endless, possibilities of phrasing. Even an electric organ, possibly one of the most mechanical instruments, in the hands of one musician can set the house on fire, and in another's, leave us yawning.

T-bone, I have the Channel Classics SACD, that is indeed a nice one, and I'll have to look for the Edgar Meyer recording. And if you haven't heard the Rachmaninoff, I think you might like it--the Steven Kates version on the Sonic Arts label from way back is a nice performance and recording (it's the one that introduced me to the piece), and there are some others out there as well.

French Horn (do you hear the fanfare?)! Combining a 4-1/2 octave range with incredible harmonic richness, a horn has a wonderful diversity of possible sounds. Brassy, lush, refined, romantic, stirring... What other instrument can migrate from the brass section in a band or orchestra to a woodwind quintet. You know you have a decent system if it can get the horn sound right. I tend to go for the classic Dennis Brain recordings, but there are many good players today, each with a unique sound.

rcprince, Edgar Meyer can make a double bass sound more delicate than I thought possible, especially in the upper registers.

2muse, I agree the French Horn is a nice instrument (and for percussives, you can always tap the side of a french horn with a drumstick)!