Doesn't sound like you need anything super small like a mini-ITX case. LAN rigs also don't need to be
that small or lightweight, like a Shuttle SFF system. And you absolutely
do not need to spend $1,000+ to make a very nice system capable of playing the games you describe and do other typical tasks. I recently built an acquaintance a LAN party system with the following:
Case:
http://www.newegg.com/Product/Produc...82E16811146065
Airflow through that is really impressive, it's light (<20 pounds assembled), isn't that expensive, and has a handle for carrying ease. Build quality was unremarkable i.e. neither underwhelming nor really impressive. I'd use it again in a heartbeat.
CPU:
http://www.newegg.com/Product/Produc...82E16819103871
Seems like everyone else here is on the Intel Sandy Bridge bandwagon but I'm not. SB is substantially more expensive, and if you're an average user, you don't need it. The X4 640 will tear through DoWII and WoW, and Star Wars: The Old Republic is definitely not going to be pushing the hardware envelope.
GPU:
http://www.newegg.com/Product/Produc...82E16814102873
The 5770 is still the de facto budget king and again, unless you're going to be playing on multiple monitors or a huge monitor (>1080p), why spend twice as much money on a video card you don't need? GPUs are totally stagnant now, they have been for a year, and they likely will be until the next generation of consoles come out...
Motherboard:
http://www.newegg.com/Product/Produc...82E16813128490
No one really knows how the AM3+ AMD CPUs are going to shake out yet, but if you must buy now, might as well get a board with the usual bells and whistles like USB3 that's compatible with AM3+ chips.
RAM: 4GB or 8GB, whatever you want to spend the money on. You likely don't need more than 4GB, but RAM is dirt, dirt cheap.
SSD : You should
definitely get an SSD if you're going to splurge somewhere on this system. If you're installing multiple games on it, you'll need a larger capacity (i.e. >120GB) SSD and those are not cheap.
HDD : You should get a disk that's big enough for what you want to store on it.
PSU: The Antec Earthwatts and TruePower New lines are great, just about anything by Seasonic is great, and the higher-end (i.e. non-Builder Series) Corsair PSUs are great. You won't need more than 400W for this system, but a 500W PSU would still be reasonable.
Optical drive: hell they're all the same Get the least expensive one you can find!
Hope this helps. I know others will chime in arguing for the latest and greatest parts that will blow all of your budget, but I'm ever the frugal advice giver because nothing depreciates in value like computer parts.