Rachmaninoff Vocalise is a nice piece, I think.....and if you are good with sibelius/finale you can even write it out in multiple keys to work out the lower and upper registers..
Rochut or Bordogni also work well to be played up or down an octave.
Jay
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Lento by Paul Holmes goes through most of the registers that you'll ever need to play in (pedal E natural up to high D on top of the first ledger line above the staff). Also the Air from Air and Bouree by Bach arr. by Bell is good. A piece good for tounging is the Rondo from the Concerto for the Double Bass by Antonio Capuzzi (but played down an octave of course).