First time builder, looking for advice

Get an Intel CPU as suppose to an AMD. They are much faster/better these days.

If you need a cheap CPU, go for an Intel i3 of some sort. They are really fast despite the price tag. A Sandy/Ivy Bridge i3 will easily beat a Phenom II x4.

Also, I suggest getting 8GB of ram. That's important depending on what you do.

Unless you plan on using more than one graphics card, a 500w PSU will be fine for you. No need for a 700w. Get a Corsair or other big-name brand. A bad PSU can ruin your whole system, so it's good to get it from a well-respected company.

What are your main uses for this build?

It's going to be mainly for gaming, although general entertainment, movies, music, etc, will be important too, hence the 1tb slave drive. And yes i was planning on using more than one graphics card, probably another NVIDIA GeForce GT 620.
Seeing as i'm looking for a quad-core processor would you recomend the sandy-bridge i5?

Okay that's helpful.

1st: I would definitely recommend a Sandy Bridge/Ivy Bridge i5 over any AMD quad-core. While the AMD will get the job done, the i5's are simply much better. Especially in games. There will be times when you will honestly see FPS differences with an i5 vs an AMD. While you may save some money now if you went with the AMD, in the long run (as you will most likely have this PC for years) the i5 will serve you much better. You won't regret choosing an i5 over an AMD. If anything, an i3 dual-core with hyperthreading will beat an AMD quad.

I would recommend any Ivy Bridge i5, or a Sandy Bridge if you can find one at a much cheaper price. Ivy Bridge is a newer architecture and just a bit faster per GHz. If you want to overclock, make sure to get the 'k' series i5's (2500k for Sandy, 3570k for Ivy).

For the graphics card, I would honestly not even get one if you are only going to spend ~$50 on a low-end. It just ins't worth the return. If you DO get a graphics card, be ready to invest at least $130-150 for a Radeon 7770 or 6850. The 7770 and 6850 are about the same performance, and are the lowest-end cards able to run most games with at least ~30 FPS. If you do a lot of demanding games, invest a good $200 or more in the graphics card.

If it saves you money, maybe just cross off the SSD for now, get a better graphics card, and upgrade to an SSD later? While I do agree that SSD's are SWEET, you need to think of necessity over luxury first.

Also, make sure you have a good 700-750W power supply if you are planning on SLI/Crossfire in the future. Look at reviews to make sure it's not a bad one, and buy from trusted companies.

Cheers for the advice, like i said the build i posted was only a rough draft and i'm most likely to be buying the components over time rather than all at once, but any input is greatly appreciated. The SSD was more of a wish than anything anyway, i've got 500GB in my current system that i'm happy to salvage across to the new ony for the time being.

I was planning on linking my graphics cards for the new system though, so (newbie question alert) could you explain what exactly the difference between SLI and Crossfire is and the pros and cons of each method?

Yeah sure.

SLI and Crossfire are essentially the same thing. What they mean is putting any 2 or more of the SAME card together in a rig for increased performance. The only major difference is that SLI is with Nvidia cards and Crossfire is with Radeon cards. While there may be (and probably is) some small technical differences here and there, they essentially come down to the same kind of setup. Neither is better/worse.

And carrying over your current 500GB hard drive is a good idea, if it is compatible. Do you know what connector it uses? If you can tell me I can find out. Holding off on the SSD is a good idea. I think SSD's are wonderful and everyone should have one eventually, but if it means a lower-end component somewhere else in the system, the SSD should be the first thing to be cut. You can always put one in later though.

Also, I recommend that you don't buy the different components over time. Reason being, if you buy piece A now, and can't afford piece B until a few months down the road, something better than piece A may come out during that time for the same price but better performance. It would make more sense to just save the funds and buy them all at once. Of course it's completely up to you though.

As for the graphics card, as I would hate for you to build a system and realize the GT 620 isn't going to hack it for you, here are my suggestions in their respective price ranges. Any of these cards will run 99% of modern games with at LEAST 30 fps, depending on the resolution/settings you run at: (oh any sorry for it being in dollars!)

Low-end/budget:
Radeon 7770 GHz Edition 1GB --- $120-150

Mid-range:
Radeon 7850 2GB --- $200-220

Upper-mid end:
Radeon 7870 2GB --- $250-260

Mid/High-end:
Radeon 7950 2GB --- $300-320

High-end:
GTX 670 2GB --- $400-420