Gnupylot is a GUI for gnuplot (the widely used multi-OS plotting utility). It's written in Python using PyQt4 libraries. With Gnupylot you can save your plots (even the datasets). It's still in Alpha stage.
Simple OS X "droplet" for quick data visualization. Drag-and-drop one or more text files containing series data and a simple scatter plot is generated containing each series with different symbols, legend, etc. GUI-less alternative to gnome PlotDrop.