Well the card you buy really depends on your budget. But I will give you a bit of info. I personally only use ATI cards, so that's what I'll talk about. The Radeon 5000 series cards have all those abilities which you described in your first post, namely they can display very high resolutions and all have HDMI, DVI, and even DisplayPort connectors. So they have you covered with many cards ranging from the 5450 (which goes for about 30-40 pounds), to the 5970 which goes for over 450 pounds. So now you have to decide which one to get, meaning how much you're willing to spend. The more expensive cards obviously perform much better than the cheaper ones, but you really have to think about how much time you spend gaming on your computer. If it's a lot, then you should go for a more expensive card (5700 or 5800), if it's not a lot then go for a cheaper card (5500 or 5600). I would stay away from the 5400 as they won't perform well in games, they are more for HTPCs than anything. Also, I wouldn't recommend the 5970 to anyone, it's far too expensive to be worth it.
I don't own any Nvidia cards but they have similar offerings to ATI, their 200 series of cards also have HDMI and DVI connectors which can display very high resolutions (though it looks like not all the cards have HDMI, so you just have to pick one that does have it).