Sound cards, unless you plan on using 5.1 / 7.1 surround in gaming. Just get a Sblive5.1, It\'s cheap and has good sound.
For the onboard nforce2, make sure it\'s MCP-T technology. Not just MCP. So your Cpu doesn\'t have to do the work. You\'ll also get onboard Dolby Digital Encoding that a Reciever can decode.
For the HD get ATA133 7200rpm etc. I\'d only go for Seagate or Western Digital.
Mem go for brands like Crucial, Kingston, Samsung. I\'ve also heard Transcend is good too. Although it didn\'t like my Kingston mem. Depending on the Motherboard u get, try to get memory that’s closest to the FSB of your motherboard/cpu. If your using Winxp, get 512 meg minimum.
As for PSU, I have a Just Cooler SP400 and it rocks. Never had any trouble with it, only stick with High-end PSU units.
As for motherboards, brands like Asus, Abit and Gigabyte are my personal favs.