The Ur-Quan Masters is a totally free port of the 3DO version of Star Control II - and its really good. Toys For Bob, the original creators of SC2 just up and gave them the source code and artwork. Although, it's not particularly 56k friendly. It can range from about 12mb to 160mb depending on what components you want to add in. If you wanna leave your net on for a while, check it out at
http://sc2.scourceforge.net/.
Also for abandonware, Abandonia is good (not as good as the underdogs though...)
www.abandonia.com.