QtiPlot!

Veusz is a GUI scientific plotting and graphing package. It is designed to produce publication-ready Postscript or PDF output. SVG, EMF and bitmap export formats are also supported. The program runs under Unix/Linux, Windows or Mac OS X, and binaries are provided. Data can be read from text, CSV or FITS files, and data can be manipulated or examined from within the application.

SciDAVis is a free application for Scientific Data Analysis and Visualization. It's an application aimed at data analysis andpublication-quality plotting. It combines a shallow learning curve andan intuitive, easy-to-use graphical user interface with powerfulfeatures such as scriptability and extensibility. Quite extensive manual can be found here: http://scidavis.sourceforge.net/help/manual/index.html

Kst is a fast, real-time large-dataset viewing and plotting tool available and has built-in data analysis functionality.Kst is moreover expandable with plugins and extensions.

SigmaPlot is a scientific data analysis and graphing software package with an intuitive interface for all your statistical analysis and graphing needs that takes you beyond simple spreadsheets and helps you to produce high-quality graphs without spending hours in front of a computer.

jHepWork is a full-featured multiplatform data-analysis framework for scientists, engineers and students. jHepWork incorporates many open-source math software packages into a coherent interface using the concept of Java scripting, rather than only-GUI or macro-based concept.

DPlot graphing software lets scientists and engineers graph, plot, analyze, and manipulate data.

Technical graphing and data analysis for Macintosh and Windows. IGOR Pro creates publication quality scientific graphics used by scientists and engineers around the world. IGOR Pro 6 is an extraordinarily powerful and extensible scientific graphing, data analysis, image processing and programming software tool for scientists and engineers.

Aveloy Graph is an application for graph creation / data visualization - fast, easy to use and interactive.