useful science programs

So, what useful, free computer programs are out there for science undergrads -that you would recommend?
I have been very happy with:
* ImageJ - for editing, viewing and merging images, especially fluorescence microscopy data (immunohistochemistry staining)
* Abiword - writing
* past.exe - simple exploratory statistics and diversity analysis: folk.uio.no/ohammer/past/download.html
* Google Scholar: often links to free pdfs of papers on author homepages

p.s.: easy cheap textbook intro in biology-oriented statistics:
"Asking questions in biology" (very cool book but it is a little lightweight on experimental design)

You're both Jews, now STFU