--removed by reborg: Do not post commercial links in this forum
You willl probably want to look at the Ultra 5 or 10 Desktops, as they are small, quiet and have low power consumption, but I've also had people take home some machines from the Workgroup and Enterprise sections for home use/learning experience.
Since you're going to be using this for Solaris 10 experience, make sure you check out
Sun's Solaris 10 Hardware Requirements to make sure you get a system with enough RAM, disk, etc. The previous link lists Solaris 10's general hardware requirements, while
this page gives a specific list of Sun systems that will run Solaris 10.