For cello solos with piano accompaniment, I recommend "Cello Solos," from Amsco Publications. The International Standard Book Number is 0.8256.2040.6, and it too is available from SHAR Music. It contains about 50 solos, some very easy, and some very difficult. A great book just to play around with.
Also, see Leonid's links to actual downloadable etudes you can play on your cello!