Software for plotting 3D-graphs



 Hi Netters!
            I'm a graduate student at the University of Illinois at Chicago
 and I'm looking for a freeware, or a public domain software to plot 3D-graphs.
 Any suggestions or help in this regard, would be greatly appreciated.
            If there is enough interest, I shall summarize the responses
 that I get on the net.
 Thanks in advance,
 -Chaya