So, in the end, I didn't build it myself (there are a number of reasons, but I'm lazy and don't feel like typing about the not-so-epic stuff).

My PC arrived today while I was in work (it was delivered there, so I had to look at the box for 3 hours before getting home to set it up). It's set up now and it is just so amazing. It (obviously) completely destroys my HP laptop, and I'm so happy I can actually do more than just surf the net and play Rome: Total War.

Here are the (key) specs:

8Gb 1333MHz DDR3 RAM
AMD Phenom II X6 1055T
ATI Radeon 5870 1GB Black Edition
22" LG 1080p Monitor (that arrived last Tuesday, was ordered elsewhere)

I'm running Windows 7 Home Premium. As I speak, I am downloading Crysis from Steam (bought while it was on sale). After that, I'll be downloading L4D2, Empire: Total War and Mass Effect, all of which were purchased during various deals.

So, anyone got any suggestions for what I should do with this PC? I feel like trying out something my old laptop could never even imagine achieving.

Congrats, though I don't see what more you need in a PC than Rome Total War....

Those are all great games to play, and the only major recomendation for a PC game I would give would be for Company of Heroes a WW2 RTS from Reliq, just amazing in every way

Try out Final Fantasy XIV in September!

Don't forget to try Witcher and King's Bounty :)

Oh yeah, get The Witcher. It is good!

that's pretty beastly and to think for the price of that you could probably have bought one of these  http://www.guru3d.com/article/asus-ares-review/1 lol... 

anyway good for you and I hope you find many games to play on it.I guess you missed portal when it was free eh pity.

You just missed Steam's big Summer sale. They had a pretty big list of heavily slashed titles. I picked up Borderlands for about $10, Bioshock 2 for $15 and a few other titles. The entire Valve back catalog was going for a ridiculous $66, which was an incredible deal for someone who has none of their games on PC.

Just be patient, shop around and pick up older games you want when they drop down in price. Steam always has their weekend deals, and don't forget deals through Amazon as well on hard retail copies. I picked up Mass Effect 2 for about $25 not long ago.

I got a few games during the Steam sale. I got L4D2, Crysis, Mass Effect and Battlefield 2. I got Portal back when it was free also, as well as the Total War pack when it was reduced (so Rome, Medieval 2 and Empire). I'm installing loads of my old games that I haven't played in years as well (Age of Empires 1/2, Rollercoaster Tycoon 1-3 and the like). Loving the PC so far.

I'm not really into RPG games, but I'm trying Mass Effect to try to gradually move towards them. I heard Mass Effect was pretty close to being a TPS, so I figure it is probably the best place to start to try and get into the RPG genre.

Mass Effect II has muc stronger shooter gameplay than the first, and looks better too. Grab it. It is so fine.

Your actually arguably better off starting with ME2 then ME1, you don't REALLY need to know the back story as they fill you in a lot.  Also ME2 is far more noob friendly.  Your rig looks pretty sweet, head on over to overclock.net and let the evil that is overclocking consume you ;)