Here are some python plotting engines/libraries:
- Older/not python dedicated:
opemath: Written by William Schelter and part of Maxima (thus also Sage) is a TCL/Tk plotting program which allows for interactive viewing. It has no separate download page. An example is this saddle: sage: maxima.eval("plot3d(2^(-u^2+v^2),[u,-1,1],[v,-1,1],[plot_format, openmath]);")
Pyqwt at http://pyqwt.sourceforge.net/ is a plotting package requiring QT. It seems to have some 3d capabilities http://pyqwt.sourceforge.net/pyqwt3d-examples.html.
Sage's plotting functionality is built on top of matplotlib, which is a very extensive plotting library with a user interface that is very similiar to Matlab's plotting. The interface that Sage provides to matplotlib is very Mathematica like.
There are also several links to plotting/graphics/data visualization programs at the scipy wiki.