usb2 card, tv card, networking card, graphics card, sound card. theres 5, but incase i would like to upgrade to n e thing e.g. digital radio card, digital tv card etc etc
wth..... new mother boards come with on board sound so u dont really need one for that all new motherboards have more than 4 usb connectors to the case graphics cards go in AGP slots, get a graphics card with tv tuner and ALL NEW motherboards have built in Nic i dont think radio cards exist and theres only one type of tv card.. u dont even need to use pci slots.
basically... what he said.. unless u want to get a PCI sound card if ur gettin a good 5.1 or 7.1 sound system for ur PC... but thats 1 slot outta the 5 or 6 on the board...