Need Advice on Gaming/Multitasking PC Build

It has been a few years since my last build, and I am looking to upgrade from a Pentium D 945 3.4ghz, 2GB PC-6400, 8600GT, etc. I am looking for some advice on my current build so far.

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APPROXIMATE PURCHASE DATE: tomorrow -- the sooner the better
BUDGET RANGE: ~US$500-750
SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: Work(Software Engineering), Gaming, Mild 2D & 3D Graphic Design, Surfing, Movies
PARTS NOT REQUIRED: Keyboard, Mouse, Monitor, Speakers, OS
PREFERRED WEBSITE(S) FOR PARTS: newegg.com
PARTS PREFERENCES: Haven't been a huge fan of ATI or AMD for a few years, but open to suggestions.
OVERCLOCKING: Maybe
SLI OR CROSSFIRE: Not planning on it
MONITOR RESOLUTION: 1680x1050
ADDITIONAL COMMENTS: Preferably cool & quiet.

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Case: Antec Three Hundred Illusion - $64.95
http://www.newegg.com/Product/Prod [...] 6811129066

HD: Western Digital Caviar Black WD5001AALS 500GB 7200 RPM SATA 3.0Gb/s - $69.99
http://www.newegg.com/Product/Prod [...] 6822136320

Memory: G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) F2-8500CL5D-4GBPK - $59.99
http://www.newegg.com/Product/Prod [...] 6820231166

CPU Cooler: XIGMATEK HDT-S1283 120mm Rifle - $36.60 + $10 MIR
http://www.newegg.com/Product/Prod [...] 6820231166

PSU & DVD/CD Combo: - $106.98 + 30$ MIR
- CORSAIR CMPSU-550VX 550W ATX12V V2.2 80 PLUS Certified
- Sony Optiarc 24X DVD/CD
http://www.newegg.com/Product/Comb [...] mbo.232789

CPU & MB Combo: $319.98 + $15 MIR
- Intel Core 2 Quad Q9550 Yorkfield 2.83GHz LGA 775 95W BX80569Q9550
- ASUS P5Q Pro Turbo LGA 775 Intel P45
http://www.newegg.com/Product/Comb [...] mbo.232667

Total Price: $658.49 After shipping with the 10$ Antec 300 promo. Also has $55 in mail in rebates.

I'm looking for any suggestions you might have on replacing any of these parts, and also for a video card. I am planning on sticking my 8600GT in here, and then grabbing a video card in a couple weeks. I want a solid video card, but I don't want to pay a ton (i.e. GTX 295). I am looking at the EVGA GeForce GTX 260 Core 216 Superclocked edition, but would take any suggestions on that as well.

As a developer I do a lot of multi-tasking. I usually have a bajillion firefox windows open, several visual studio, netbeans, or eclipse windows open, etc, but I also do a fair amount of gaming.

I would like to stay below or at 700$ without a video card.
I have a couple 22" Acers that I will be hooking this up to. I may upgrade those some time in the future.
I want performance, but I'm not ready to pay for a core i7.
I would also like the computer to be cool and quiet.

Thanks for taking the time to look at my build!

^+1 for the i5 recommendation... For the HDD though, this one is actually much newer, faster, and more efficient than even the WD:
SAMSUNG Spinpoint F3 HD502HJ 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal
http://www.newegg.com/Product/Prod [...] f3%20500gb

Yep...another +1 for the 640GB black - fantastic drive.

Looks like a solid build. If you live anywhere near a microcenter, you can get the Q9550 for $170.

jbakerlent - can you point me to articles to read on this. I haven't seen anything about them.

Thanks

Do you guys have any recommendations/prices on i5 compatible motherboards?

Ahh thanks, that's what I was thinking.