Scientific Visualization packages?

I wonder what everyone is using for plotting scientific data. Especially, for plotting field data. I use MWS and fullwave for simulations. But somehow, in my opinion the visualization and plotting capabilities of these programs are somewhat limited and not very flexible. I usually use matlab. But it has its problems. It is very slow, needs a lot of memory. I would be grateful for better suggestions

If you can covert the output to HDF5 format there are many open-source (free!) tools that can be used for visulization.
Here's a link:
http://hdf.ncsa.uiuc.edu/hdf5

Also. a good place to find out more about this is the MPB newsgroups. You can access it at: gmane.comp.science.photonic-bands

Also, the above are for plotting and manipulating field data mainly. Matlab's pretty good and also pretty standard for plotting 2D and 3D graphs. Another alternative could be GNU Octave. It's free and is supposed to have the same capabilties as Matlab. There's GNU Plot too. Check http://www.sf.net for opensource projects.

mayavi is prefered