You need one of thos LPX or NLX desktop 'book' PC cases, that are not much big than a floppy drive layed out next to a CDROM drive. The expansion cards fit on a riser, so are parrallel to the motherboard.There's a website that specialises in selling NLX/LPX cases & motherboards, but I forgot its name/address. Most LPX & NLX motherboards have intergrated Video, Sound, plus some even have intergrated nics & modems, However they do sell some that have AGP slots on the riser card. They have a huge range at that website I can't remember the name of. LPX systems will useally have greater expansion potential than NLX cases, as they often have slots on both sides of the riser card, while with NLX systems, they only have 2 or 3 slots on just one side of the riser card. However NLX systems are much easier to work on & upgrade as the case LED & switch wires & IDE cables, plug into the back of the riser, which has a slot at the bottom, that a edge connector on the side of the motherboard slides into - so when upgradeing you can slide the old motherboard out & slide the new one in without removing anything, except perhaps the heatsink & RAM, actually some NLX cases are designed so you don't even need to open them to slide the main board in or out.
Heres an example of a good NLX case
http://enlightcorp.com/pc_cases/7800.shtml
Also the new FlexATX standard might do you
Heres the link for the Elan Vital (Asus) FlexATX case.
http://www.elanvital.com.tw/products/pccases/B-9F.htm
BTW, you'll probably get more informative responces if you posted this at the cases 'n cooling forum, & I suggest you check the 'Case 'n cooling fetish' forum at
http://www.arstechnica.com.