What should I upgrade next?

Okay, I am in a constant state of feeling like my computer needs to be upgraded. I want to upgrade it next time I get a chance, but I'm unsure of where to go. I wanted to go with 7.1 sound, but I want another opinion from better people who know more (you guys ) in case there's something more important that I'm missing.

Mobo - ECS nForce 570 SLIT-A Socket 775 Motherboard
CPU - Intel Pentium D 830 3.0gGHz DT 800FSB Socket 775
Speakers - Logitech X230 PC Multimedia Speaker System-32 Watt 3pc
Sound Card - none; integrated
Optical Drive - NEC ND-3550 Black 16x DVD Burner in Retail Box
Monitor - HANNS-G HN199D 19in 8ms DVI LCD Monitor w/ Spks
Hard Drives - Maxtor 160GB EIDE HD 7200/16MB/ATA-133 AND WD Caviar 250GB SATA-3G HD 7200/16MB/SATA-3G
Case - Aspire X-Discovery Black Case w/o PSU
RAM - OCZ XTC 2048MB PC5400 DDR2 667MHz (2x1024MB) AND PQI 1024MB Dual Channel DDR2 PC5400 667MHz (2x512)
Video Card - EVGA GeForce 8800 GTS Superclocked 640MB PCIe
PSU - Ultra XVS 700w Modular PSU Black

Thanks a lot!

biggest increase in performance would definitely be upgrading cpu to Core 2 duo or quad core Q6600 depends on budget. Cheapest Core 2 will still beat a D 830..and they overclock like crazy

C2D indeed. It would also serve you justice to get a better quality MB.

If you want a good 7.1 sound card then you gonna have to match that with a good set of 7.1 speakers.

Cool...thanks y'all! I saw your suggestions, and I went crazy shopping for new stuff...whaddya think? (I didn't get it yet)

MOBO - ASUS P5K LGA 775 Intel P35 ATX Intel Motherboard
HEATSINK - Thermalright Ultra-120 Extreme CPU Cooler
CPU - Intel Core 2 Quad Q6600 2.40GHz
MEMORY - OCZ Platinum 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) x2

I was going to go for the new DDR3 memory and the board to match, but I saw in another article, that after some pretty thorough tests, higher end DDR2 was still better than current DDR3 according to bandwidth and latency values...