You have some really good choices already. I LOVE the q6600. If I could suggest the ABIT IN9 32X-MAX LGA 775 Nvidia nForce 680i SLI / NF590 SLI ATX Intel Motherboard - Retail
http://www.newegg.com/product/product.aspx?Item=N82E16813127020
I linked that from newegg but they no longer carry it. That is basically a server board that was switched to home use (much like the AMD 1207 FX chips, if you know what that is). I put that in my ladies pc and it is rock solid, can run up to 32gb of ram (why anyone would need that) and has true load balancing of the NIC (which is a first for me).
Ram, go with 4gb. At 100 dollars right now, it doesn't get much better. Just remember that you will need a 64-bit OS if your going to want to utilize all 4gb. A 9XXX series Nvidia is good, but I still love the 8800GT.
I didn't see budget or purpose but get a good case/power supply. I like the P series from Antec, dead quiet and pretty nice looking. Power supplies are as important as a hard drive, cpu or motherboard. Get something high end or everything suffors. A 550watt name brand is going to be better than a 700 watt no name.
Built in sound usually works for me, although I do have a few X-fi's around. I know i'm forgetting things but if you really need some help with a build send me a budget and what you need the pc for and I'll find some links for you (Monday's are SLLLLLOOOW at work lol). I don't build for people I don't know but I can get you all the links, I think it is fun LOL.