I think SSD's offer still the biggest boost compared to any other hardware upgrade. Prices have been steadily falling over the last few month and seem to continue this trend. Especially now as 2xnm NAND parts become available. OCZ for example offers a 60GB Vertex for $109 which is almost 50% less than just a couple of month ago.

SSD is just a dream unless your rich. After a few years the price is still to high to justify, at least for me. HHD have never been lower.