Thank you for your answers. Helge Egil, actually I meant scientific plots in 2D. Nothing very advanced. Jiri, I will start trying with Gnuplot. Thanks!
if you google "Gnuplot tutorial " or "Gnuplot examples " then you can get more specific examples. I do have some example at my RG profile how to create hundreds of plots from input data in automatic mode under LINUX. This feature is really cool. Once you define your plot, it can be run on new data automatically! :-) It saves a huge amount of time.
For 2D and some basic 3D Graphics, Adobe Photoshop and Illustrator(2D Only) are the best softwares. Gimp and Inkscape are best among free Softwares. Gimp is similar to Photoshop. Corel Draw is also an option.
Adobe Photoshop is best among all.
For 3D Graphics & Animation and 2D animation there are other softwares.