Newbie to newbie:
1. Do you care how quiet your computer is?
2. Need more disk space? I'd go for a nice fast 500GB or 750GB HD unless you want to spring for a Raptor.
3. Can you find a good deal on DDR2-1066 memory? I got in on a good deal on a pair of Crucial Ballistix for $89 after rebate. Having the extra headroom makes it easy for me to overclock without having to fiddle with the ratios too much.
3. General advice: rather than build something to last 4-5 years, I'd go for "cheap and disposable" and upgrade something or other every year or two. That said, the Q6600 is great; Mobo is fantastic but if it were me I'd either go cheaper or get a hybrid DDR2/DDR3 board; I love my eVGA 8800GTs.
I'm currently OC'ing my E4300 to 3ghz on stock cooling, but I don't know anyone who would overclock a quad with stock cooling. You can get a nice HSF for <$50 and since you're paying $300 for your CPU, I think a better HSF is a wise investment.
For reference, my E4300 was 114 USD. I still intend to get a Ninja Mini for it when that HSF becomes available.