Your setup generally looks good, but here is some advice:
The Centurion 5 is a nice case, but it's fairly old now and the lack of a 120mm fan slot in the front is a bit annoying. I got one almost three years ago for my other system. Look at their new RC-690 instead, which is not much more expensive and has better cooling options.
Don't spend more than $150 or so on the motherboard unless you have maxed out everything else. The expensive boards offer very little over the cheap ones. The 680i chipset is also generally inferior to the P35 and X38. Even if you want to overclock, something like an $80 IP35-E can max out almost any processor available right now, at least on air cooling.
The 8800GTs are hard to come by right now and are being gouged a fair bit. It looks like we're seeing a repeat of the 7900 launch, when the cards were vaporware for the first few weeks. You're better off waiting for the new GTS in a few weeks anyway and seeing how it performs.
That monitor is rather lousy given the rest of your system. Look at the 20WMGX2, which is still probably the best all-round LCD available. It's $360 on Newegg, although that is after a $100 rebate. There is also a 24" Soyo on OfficeMax that is quite a steal, an S-PVA panel for $300, but there is always the issue of being stuck at a high resolution with such a monitor and having to upgrade frequently. In any case, with a $1500 budget you should definitely get a better monitor.
The other components are good, but you're paying too much for some of them. The HX520 is $96 on Buy.com and the memory you listed should be about $120-140 on Newegg depending on the particular variety. Memory in general is another thing you don't want to spend much on, as any 800mhz memory will max out a 9x multiplier processor easily and you hardly get anything in the way of added real-world performance beyond about 700mhz.
