AMD Llano is great. I got a similar build to this one below just recently and love it. The kids can play Sims3 and Portal2 no problem, without a dedicated graphics card. The APU graphics are that good. The cpu horsepower is not a problem for us. Pretty darn fast response time actually. Benches are really for the hardcore dedicated gamer or performance user, not the average joe.
This can be upgraded with a Quad core cpu, more memory and a graphics card in a modified Crossfire arrangement with the APU.
AMD A6-3500 Llano 2.1GHz (2.4GHz Max Turbo) Socket FM1 65W Triple-Core Desktop APU with DirectX 11 Graphic - $89.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103951
ECS A75F-A FM1 AMD A75 (Hudson D3) HDMI SATA 6Gb/s USB 3.0 ATX AMD Motherboard- $74.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16813135293
Memory is important with Llano, that's why there is 8GB, Cas Latency 8. If you have XP, the OS won't recognize anything above 4GB. Slightly less than 4 GB actually.
Patriot Viper Xtreme Series, Division 2 Edition 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory - $49.99 + $15 MIR
http://www.newegg.com/Product/Product.aspx?Item=N82E16820220561
CORSAIR Builder Series CX500 V2 500W ATX12V v2.3 80 PLUS Certified Active PFC Power Supply- $59.99 + $20 MIR
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139027
LITE-ON DVD Burner- $19.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16827106289
Rosewill REDBONE Black SECC Steel ATX Mid Tower Computer Case- $39.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16811147159
I just liked that case, there seemed to be a lot of features for the price and kind of cool looking too. But any case around that price will do. Just make sure it has a couple of fans, preferably one in front and one in the rear for the best airflow.
Subtotal: $334.94
No tax with Newegg
Approximate shipping cost: $12.32
Total: $347.96