Do you have a graphics card without a DVI port, or is this a 2nd or 3rd monitor?
I know some of the new top end cards are starting to come out with only HDMI and display port, but if you had one of those very expensive cards, I would be very surprised at your choice of monitor.
If you have a DVI port on your card that you can use, then get a straight DVI cable, otherwise a HDMI to DVI is the way to go.