For most people, the first thing to buy these days should be a SSD. The only downside is that the ones you don't need to manage are the Sandcore series. For the rest, you need to do maintenance on them regularly or your speed starts to crawl. On my regular SSD, I usually zero out free space once per week and run Snow Leopard Cache Cleaner to optimize (defragment) at the end of a heavy work day where I do many reads and writes to the drive. So far my speed is around 230 read 190 write and if it drops I can get it back up there after maintenance.