Aside form the Human voice...

My vote goes to the kazoo. Spoons would be a close second.

lets offer up jimi hendrix as evidence. there are lots of great 'expressive pianists' but jeez louise, to this day what he did with an electric guitar is still looked upon as more than skill....how about magic?

Tabs, if you listen to the Rachmaninoff cello sonata, or Bruch's Kol Nidrei, or the Elgar cello concerto, you'll see the vast range of emotion that can be brought out of a cello. Maybe leaning towards the melancholy a little, but it just strikes home to me. It resonates so beautifully too--I won a cello lesson from one of our NJSO musicians in a silent auction and got to play it for the first time, you can't believe how it resonates through you when you play it. And it's not just the notes (the lows and the highs) and the ability to bend and finesse them like you can with the guitar, the bowing gives the artist the ability to play with phrasing, both in timing and in terms of volume and texture. You could say the same about a violin in most ways, but it doesn't reach the low notes that stir the soul (or at least mine)....

Nuguy, I have a record of the Temple City Kazoo Orchestra, to say that listening to them play is an emotional experience is an understatement.

None. It's the instrumentalist, a.k.a. the musician, that expresses.

Given Ojgalli's caveat, and assuming an equally expressive musician per instrument, which instrument has the most room for expression? I would agree with Rcprince and say cello (and a close second probably goes to ptmconsulting's sax suggestion).

The big "problem" with piano (and therefore organ) IMO is that it is percussive only. Sax has the wind control (and reed control on top of that) which allows for continuity of varying types/degrees (with discrete note separation or note melding using "glissando"). It's in the same general register as the human voice, and covers a wide (3) octave range with a tone ranging from sweet to raunchy. However, sax is not percussive. Cello probably has a slightly wider range (usually 4 octaves) and notes are either discrete or completely run-together. Cello lacks the ability to get super "raunchy" the way saxophone can but the player can both 'push' and 'pull' the instrument for richness of tone, dynamic control is far better, vibrato is probably best in the orchestra, and a single player can be either Isaac Freeman (the bass for the Fairfield Four) or the sweetest, most delicate alto, AND everything in between.

rcprince, I completely agree about the Elgar and Bruch. Among expressive cello, I also like Peter Wispelwey's playing of Benjamin Britten Cello Suites on Channel Classics, Mario Brunello's odd compilation called "Alone" (tough to find in the US sometimes), Schelomo Rhapsody by Ernst Bloch (same dark vein as the Bruch), and Edgar Meyer's rendition of Bach Unaccompanied Cello Suites (on double bass), which is a something of a shocker if you find low notes stir the soul. The last stays high on my playlist no matter how many times I consciously try to "take a vacation" from it.