A/V port is so common that almost all digital video camera support A/V output.
Advantage: AV cable supports long distance transfer at low price.
Disadvantage: AV grabbing card uses analog signal, whose quality is inferior to 1394 card.

To use A/V input for the software, you should buy an AV grabbing card:
AV grabbing card: widely available on the market.

1394 card has been the standard interface in video field, which is supported by most professional or personal cameras, and notebook computer also is configured with the port as a standard.
Advantages: higher quality signal that is digitally transferred, suitable for professional users.
Disadvantages: shorter transfer distance, 1394 relay is needed to prolong the effective distance, so the price is higher. One 1394 card can only connect to one DV.

To use 1394 card for the software, you should buy a 1394 card/grabbing card:
Notebook computer: need a PCMICA 1394 card (all notebooks contain 1394 port)
Desktop computer: need a PCI/PCI-E 1394 card
At present, it is recommended to use one card for one DV, it is not recommended to use cascade connection via such as 1394 HUB or to connect all the ports of the card to DVs

To prolong the 1394 connection distance, you need by a relay :
Due to the signal attenuation in 1394 cable, it is better not to connect for longer distance, or it is recommended to use 1394 cable with DV relay to connect the camera, thus the distance can be as long as 200m without signal attenuation.

SDI port is widely used at broadcasting level, e.g. television stations.
Advantage: support SDI signal I/O and other broadcasting level equipment
Disadvantage: expensive.

You can find some video capture card here:
http://www.ramelectronics.net
 
http://www.pinnaclesys.com
 
http://www.ramelectronics.net/html/video_capture.html