Stay away from the Intel GMA X4500 graphics core. It is not meant for games. Since I don't know what your budget is I'll just make some general recommendations.
If you have a $700 budget, then the following CyberpowerPC Gamer Xtreme 1314 is a pretty decent deal.
http://www.newegg.com/Product/Product.aspx?Item=N82E16883229266
+ It has a Core i5-2300 CPU which is part of Intel's current line up of CPUs. It is a quad core CPU as opposed to the single core CPU that you currently have now. Generally speaking it should be more than enough processing power than you need unless you play games. Most games only use two cores; it seems Cities XL only uses one core. Generally, the more cores you have the more fluid the operating system (Windows 7) will feel.
+ The Radeon HD 6670 is a mainstream video card that will be more than enough for Cities XL. It can handle more demanding games quite well like Crysis 2, and Metro 2033 if you do not set the graphics quality too high. If you are into more mainstream games like the Sims 3 then this video will be fine and should last you a long time.
+ 8GB of RAM will be more than enough for your needs. 4GB of RAM is generally the minimum recommendation.
+ This "Sandy Bridge" Core i5 CPU also has the Intel HD 2000 graphics core. It's a little better than their old GMA X4500 graphics core, but still not really meant for playing games. Not that it matters though since this PC comes with the HD 6670 graphics card.
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The iBUYPOWER Gamer Power 567D3 is less expensive at $440 after a $40 rebate if you are on a budget. It is certainly more powerful than what you currently have, but not as powerful as the CyberpowerPC mentioned above.
http://www.newegg.com/Product/Product.aspx?Item=N82E16883227314&Tpk=iBUYPOWER%20Gamer%20Power%20567D3
+ It comes with an AMD Phenom II X4 925 which is a quad core CPU. It is certainly not as powerful as the Intel Core i5 CPU, but it is more than enough for your apparent needs.
+ The ATI Radeon HD 5570 is definitely less powerful than the HD 6670, but it is still more than enough for Cities XL. It's graphics power is roughly half of the HD 6670.
+ It comes with the minimum recommended 4GB of RAM.
+ This is certainly a bargain system compared to the CyberPowerPC so overall performance is lower to match the lower price point. But the good news is that it is more than enough for Cities XL.
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The CyberpowerPC Gamer Ultra 2093 sells for $600 which is a somewhat decent computer for games.
http://www.newegg.com/Product/Product.aspx?Item=N82E16883229280
+ It uses AMD's new Llano chip, the A8-3850 which is a combined CPU (4 cores) and graphics core on one chip. Similar to the Intel Core i5 CPU as mentioned above. However, instead of combining a powerful CPU and a weak graphics core, AMD's Llano processors combines a relatively weak CPU with a relatively powerful graphics core. The CPU core is not as powerful AMD Phenom II X4 925.
+ The Radeon HD 6550D graphics core is probably in line with the HD 5570 in the iBUYPOWER PC above. Maybe slightly faster.
+ It comes with 8GB of RAM which is more than enough for your needs.
+ Overall, this is not much of a deal considering what you are getting for $600. The cheaper iBUYPOWER has a better CPU and the Radeon HD 5570 is more or less on par with the Radeon HD 6550D that is integrated into the A8-3850 processor (AMD calls it an APU). You could just the iBUYPOWER PC for $440, use $160 to buy more RAM and a more powerful video card which turns that PC into a better deal this this Cyberpower PC. Of course you would need to install the RAM and video card yourself; not a difficult task.
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Based on the computers listed on NewEgg, there is not really much of a deal on a PC for less than $400. You would be seriously limiting yourself to PCs with much weaker CPUs and video cards. In the $500 - $600 range, NewEgg doesn't have much either in terms of a PC for playing games. You can buy a PC with a powerful CPU, but then you are lacking in video card area.
I have mentioned that a quad core CPU is generally more than enough for your apparent needs. So why did I only mention PCs with quad cores? Well, all the dual core PCs lacked a decent graphics card for casual gaming. You can certainly purchase your own video card and install it yourself, but I'm trying to make this a easy as possible.
To sum up, if you have $700, then buy the CyberpowerPC Gamer Xtreme 1314. It should last you a long time based on your current usage and will be "future proof" for upcoming causal games. Although, "future proof" is a bit of an oxymoron when you are talking about technology. If you don't have $700, and $440 (after rebate) sounds more sensible to you, then iBUYPOWER Gamer Power 567D3 is the way to go. You are not really going to notice the difference in processing power based on your simple usage, the video card should be good enough for your needs unless you start playing more complex games. Besides, you can always buy and install a video card yourself if you find that the Radeon HD 5570 is starting to get too slow for your needs. Just post a question in this forum before doing so. I've seen quite a few times where someone thought they purchased an upgraded video card, when in fact it was actually a downgrade in performance.
So where does that leave the CyberpowerPC Gamer Ultra 2093 with the A8-3850 APU for $600? Don't even bother with it. You are basically paying a premium price for overall lower performance. The real value of the Llano APUs are with value oriented laptops for games, not in a desktop.