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Try using a 660 or 670 for the GPU instead. They are made better for gaming. 640 is more for general use.
Also, no casing? There's also the monitor issue.

It's hard to recommend parts without a price range.
Oh, and if you're outside of North America do you have any sites that you buy parts from?

build a new oil rig

Tell us your budget and what will you do mostly with your PC.

you need to set a budget, expectation and needs help with that.
and whatever hardware you will get from your old PC to count out.

Here's one website that may help you out

CPU: Intel Core I3 3220 - £93.39
MB: ASROCK B75 PRO3 - £60
RAM: GSkill 8GB (2x4GB) - £52
GPU: Asus or Gigabyte AMD Radeon HD 7850 1G - £140.00
SSD: Crucial M4 64GB - £56.97
HDD: Your own hard-rive
PSU: Antec VP350P 350W - £37.82
Price from Amazon.co.uk
Total: £440.18
If you want new HDD: Seagate 1TB +£48.8
If you want new Case: +£40 - 50
If you don't want SSD speed, remove it and get you £57 less, but I highly recommend it

CPU: AMD Phenom II X4 965 Black Edition
Motherboard: Gigabyte GA-78LMT-USB3
RAM: Corsair CMV4GX3M2A1333C9
HDD: Hitachi Deskstar 7K1000.C, 500GB
GPU: Sapphire HD 7850 1GB GDDR5
Computer Case: Cooler Master Elite 344 USB 3.0
PSU: Corsair Builder CX430 Bronze

I just dropped by to say don't get a "GT" graphics card by NVIDIA for gaming. At a minimum you should be looking at the GTX 650 (or higher).

As others have noted above there are some great builds you can make for well under your price point. Some decent ATI/AMD options exist as well around that price point, and if I remember right the current ATI/AMD offerings are actually quite competitive at that price range. While I'm personally an NVIDIA guy (have been since the 8800's came out over 6 years ago) I know the ATI/AMD cards are pretty decent right now. If you're looking to do any Bitcoin mining it's worth noting that NVIDIA cards are TERRIBLE for Bitcoins--I don't do Bitcoin stuff but I wanted to make sure it was mentioned.

I bought my computer parts on the 18th this month and haven't been able to build it. Now today I finally have all day to build it, but I can't find my Windows 7 disk (read: too lazy to look) and I don't have enough HD space to download it off the internet

You wont need an aftermarket CPU cooler if you aren't planning on overclocking your cpu, and you wont need a cpu with an unlocked multiplier (typically indicated by the "k" on intel cpu's) either if you aren't planning on overclocking. And a gtx 660/660ti/670/680 would be a better choice unless you are planning on buying a seriously underpowered cpu. And if you have a spare bit of cash, add in a solid state drive, you wont regret it.

If you aren't planning to overclock, the best option, if you insist on having your own choice for CPU cooler, is the CoolerMaster Hyper 212 EVO. It is cheap and will allow overclocking, later. You don't need it, though, unless you plan to ever actually do it. You could always switch it out, later.

The 640 is weak, I would also go AMD and higher up the chain. You get games and usually a lower price. Great overall deals. Try this chart, to show you the different tiers. I recommend at least a 7850, from AMD, with the game bundle attached (Not all places will always have the bundle). Sapphire, MSI, Gigabyte, and Asus are some great AMD companies.

There is nothing wrong with Seagate drives, although Western Digital might be slightly better. I use a Seagate 3tb, personally. The 3tbs have been dropping down, like crazy, here in the states, so keep an eye out for sales on any size. It doesn't matter where you are, there should be some good occasional sales on any size drive you want.

CoolerMaster makes alright power supplies, I would go Corsair, Seasonic, or Antec first. Price at the time of sale, since they always have great rebates. I got a 1200W power supply for less than most 850W ones were, just by hitting a sale. You should easily be able to find a 500-850W priced way down. Make sure to look up some reviews and make sure everything is good. You want ability to hit power promised, ability to maintain it, and also power savings, when possible, among other things. They have some great review sites, like JohnnyGuru. You can just type a product name and the word review into Google and usually trip upon some decent sites, where you can compile information.

wait 1 week or until june 3rd for intel haswell

How about a HD 7770 and an AMD Phenom II x4 Black Edition?
Cheap things imo, both work great.

Get an AMD APU if you want to go cheap! :D

http://www.newegg.com/Product/Product.aspx?Item=N82E16819113280