I'm sorry to disagree with you desired but from what I've been able to see PCI Express cards are more common than their AGP equivalents as well as generally being cheaper. Whatever motherboard you buy, and I've no particular preference, ensure it has PCI Express, you can get a cheap PCIE card for about £30. Since you're interested in video suggest that you try to get a motherboard with Firewire as well as USB 2.0 and personally I'd be looking for a motherboard that can take SATA drives as well as IDE ones as they're faster and are reasonably priced now.
There are socket 939 motherboard that do take AGP but I think later on you might regret getting one though I suppose it depends on what you use it for. Lastly although I have no particular preference regarding make, I'd buy a good brand and the ones I've been looking at at the moment as I've been considering upgrading are the MSI ones. Heres one with AGP for £58 click here though they are awaiting stock just now or have a look here click here and here click here and here click here and here click here