Until GTO can provide a more informative answer here are some thoughts.
The choice of case and motherboard are important and will influence your other options. Here are two scenarios:
Micro ATX MB: Gigabyte GA-H55M-UD2H, ticks all the boxes except for USB3.0, allows up to 16GB of RAM and Intel i3,i5 and i7 processors
Case: Antec NSK 2480, Includes a 280 Watt EarthWatt PSU, Micro ATX boards. Note air vent on top of case.
ATX MB: Gigabyte GA-H55-USB3, should do everything you need and includes 2 x USB3.0 ports
Needs a bigger case: LianLi PC-C32 a fine case but no PSU included.
The first option has an inexpensive case but lacks USB 3.0. Will the larger Lian Li case, and more expensive option, fit under your desktop stand?
Both options rely on the inbuilt MB Intel graphics which should be OK if you are not into gaming.
I have to admit to being an Intel, Antec and Gigabyte fan so this no doubt excludes many other good solutions. I assume you are not looking for a commercial solution from Dell, HP, Acer etc.http://www.gigabyte.com.tw/Products/Mot ... uctID=3309http://www.gigabyte.com.tw/Products/Mot ... A-H55-USB3http://www.antec.com/Believe_it/product.php?id=MTE0Nw==http://www.pccasegear.com/index.php?mai ... ts_id=5979