Gnu/Linux software: Calculus, Algebra, Graphing

Hi. I'm taking Calc II right now. I haven't done anything more advanced like statistics classes or anything. I use my TI-89 ALOT, in particular for calculating derivatives and integrals, and to get simplifications of algebraic and trigonometric functions. (Usually to double check solutions I've already worked out.) I'm also a pretty avid FOSS/Linux user, and I'm wanting to find (FOSS) software that will do basically the same thing on my Linux workstation. However, there seem to be so many things out there labeled as mathematical, computer algebra, or graphing software, that I'm not sure which one to invest my time in. A few of the ones I've heard of are Octave, Maxima, Sage, and SymPy. I'd appreciate if someone could point me in the right direction.