I wanted to go for Cooler Master CM 690 plus Antec Earthwatts 500w instead, but I can't justify the price. This comes up to around 1000 bucks, but I don't know if there's anything that can be improved or anything I've done wrong.
I'd switch the board for a Gigabyte GA-790XTA-UD4. It's more future proof with USB 3/SATA III support and it supports Crossfire.
Switch the WD HDD for a Samsung Spinpoint F3 500 GB. It's faster and cheaper.
I'd highly recommend stepping up to at least the HD 5770. It's quite a bit more powerful and not much more expensive. Neither the 5750 or 5770 will really game at 1080p though. You'll want to add a second one soon (which is why I added a Crossfire board). If you were to stick to the 5750, adding the second one would only help for a couple of years before it was too weak. With the 5770, it would last much longer.
Due to the need to Crossfire, I'd also increase the PSU. Grab a 650W unit from Corsair, Antec, Silverstone, SeaSonic, or XFX to ensure quality. You could get a 700W unit from OCZ too, but that's a bit of a step down on quality.
Some other cases to look at are the Coolermaster Centurion 5, Antec 300, and Antec 300 Illusion. They should be cheaper, and are still high quality.
Sounds good, but those upgrades are really expensive - because of supply of components in NZ, some things cost more than they should. For example, the 5750 costs around $200 and the 5770 costs around $275, which is quite a bit more. Also that motherboard costs $300 dollars here
It seems the Asus M4A87TD motherboard I linked supports USB3 and SATA 6.0GB/s, so I'll probably go for that one.
And note that I would like to play games at 1080p, but frame rates are more important than graphic quality to me, in the future I can spend more on graphics cards but since this is the first build I have to buy quite a lot of parts.
Having said that, is it just me or are the hd4850, hd5750 and gts250 very similar in performance? GTS250 is the cheapest one for me, so am I right in thinking it would be the best choice?
Also thanks for the case and HDD recommendations (:
Edit: Just realized I'd linked the wrong product page for the M4A87TD mobo. Changed it.
Technically you could Crossfire two cards, however they would be working at x4/x4 not x16/x16, so people tend to avoid that as it does effect performance.
Having said that, I believe the more powerful the card the more effected they are by the lane speeds. As you are planning to use a fairly weakish card, they may not be as effected by the slower lanes and you may be able two XFire without losing much performance (This is purely guessing, I have never tried two weak cards in an x4/x4)