SSDs are mostly good if you need fast read or write speeds, eg watching or editing large files like raw audio or video. They won't help much for standard stuff, and are one of the larger premium price points. They are very nice in that they produce less heat and are more stable, no spinning discs, but you won't notice much of a performance gain for general use.
The biggest bang for your buck is RAM. I always get as much RAM as I can afford. That will improve performance of everything on the system. Upgrade CPU/cores next, for overall performance.
Again, depending on what you're doing, the graphics card can make as big a difference as anything else. That's mostly for gaming and video playing/editing, however. But with more and more video streaming going on, the graphics card can be very helpful to improve performance and quality.