I'm using
Gnumeric, because it's small & free. It acts a lot like Excel, but for now it's getting the job done. The graphics are fair.
I've used MS Excel before and I like it, the graphics are better than Gnumeric, but I still have trouble displaying data the way I would like. The graphics are kind of semi-automatic and there are places where I would like to be able to tweak, I can't. I don't know if it's a limitation of the program or the user.
I keep think that there is something out there that would give me awsome control, and still be open source, but I haven't found it yet.
-AC_Hacker