Strongly seconding the SSD recomendation. I can't think of anything else that's given so much enjoyment for the money. A SSD dramatically increases perceived performance of a computer beyond what you'd expect from benchmarks. Adding extra ram can hide the latency of a mechanical HD by caching, but it does nothing for worst case performance, and worst case performance is highly salient. I'd much rather use a low spec PC with a SSD than a high spec PC with a mechanical HD. Predictably mediocre performance feels faster than high average performance with high variance.