PCI Express has been the dominant method of connecting a video card to a motherboard for about five years now. Every high-end video card is released with the use of a PCI Express x16 slot in mind. There are, however, a sizable number of people who have computers which are old enough that a PCI Express slot may not be available.
In most cases, computers which do not have a PCI Express x16 slot available instead have its predecessor, known as an Advanced Graphics Port. An AGP is very similar visually to a PCI Express slot, but the two are not compatible with one another. This means people who have older computers are often limited in selecting a new video card. This is more common than one might think, as processors are not a major factor in the performance of many video games, whereas video cards are.
Finding modern AGP cards can be difficult, but they do exist. The three cards listed here are great bets for those needing an AGP video card. It should be noted that ATI wins all of the top slots because they are the only company making reasonably modern AGP cards. Also, AGP cards carry a price premium due to their low manufacturing volume, which is why these prices will appear inflated next to the prices for modern PCI Express video cards.