You will often hear the term "publication-quality" graphs when you come to publish your research results. This mainly means, non-excel graphs, which up to now are very primitive and non-profesional looking. Therefore you will have to use programs such as grace, or R to obtain your "publication-quality" graphs. The praise for the latter program has even reached the headlines of the science pages of the New York Times news paper.
sudo yum install r grace sudo apt-get install r grace