Black Magic Design (www.blackmagic-design.com) make a USB3 capture card that will capture SD and HDMI inputs. The other option I know of is the epiphan range of DVI framegrabbers - they have a DVI2USB option. Howver I have heard reports that the epiphans don't necessarily capture great quality but have been unable to test this myself. The epiphan devices cost about 4x the black magic devices.
If you have a very recent Mac model that has the new thunderbolt interface then Black Magic also have a thunderbolt version of the Intensity capture device. If I had money for a new laptop and a new cap device, I would be getting a MacBook Pro and thunderbolt intensity card.