to answer your question, we have to know which aspect of cytoskeleton you like to study. There is the MT cytoskeleton as mentioned by Louis, and the stentor is really a fascinating object to study.
then there is the actin cytoskeleton, where keratocytes are one of the model cell lines for branched actin networks.
and then, there is also a spectrin cytoskeleton, which is dominant in red blood cells.