What scientific plotting software is available?

I am currently doing some experimental work and I have a lot of data to trawl though. I use Gnumeric, and it's very good, but often I feel there has to be something better.

Ideally I would like the maximum number of features with a minimal learning curve, but really I'd just like to know if there is something better than Gnumeric that I can use for manipulating and plotting data.

What would you recommend?

I am a Physics student and found that the best scientific plotting software for Ubuntu is QtiPlot. It is very similar to Origin, and works really well.

Numpy and Matplotlib make a good combination for processing and displaying data.

I would suggest Gnuplot. It has a nifty set of features and is good documented. So if you take some minutes to skim through the documentation you'll get the basic idea. I use gnuplot for nearly all my plots, only when I don't need the full set of features I tend to use TikZ from LaTeX.

The R language is also quite popular and can be combined with Sweave for use with Latex.