1) Clipless shoes and pedals. This will give you a much better contact with your pedals and an improvement in transfer of power.
3) Shifter upgrade. Going from 8 speeds to 9 speeds is nice but not a real big deal.
2) Computer upgrade to cadence can be invaluable if you are working on improving your cadence. If not, don't bother.
5) Altimeter with memory. A nice thing to fool around with once you have everything else.
6) Fenders. Only if you ride often in rain. I have never used fenders and I have, oh, I guess about 20 rainy rides this year maybe more and some in near deluges. Now I can understand having fenders if you ride frequently on nasty sloppy roads especially if you are a commuter.
4) Rear Rack and trunk. If you do long rides and have a real need to be self contained, this can be invaluable. Otherwise, it can be just added weight.