Maxima. Nice book with many examples of how to use Maxima. Since the Schockwellenreiter just wrote about Maxima again and I liked the wxMaxima interface in his post quite a bit (and unlike some other programs, it also looks good on OSX), I will probably play around with it a bit. Especially since it is much slimmer than Sage (even if it of course can do much more, as it integrates many other math packages).