That really depends on the lines you want to hook up to. If you want to do Video Calls over a normal phone line, then you'll need something like a TDM card, personally I recommend Digium Cards. (link) They kinda started the asterisk game and I've never had a problem with any of their cards.
However there is no special hardware required to make or recieve a video call, Asterisk simply connects the calls. Most SIP providers allow video calls, so i'd suggest going with one of them, and just make sure your internet connection is capable of handling the load.
Add (see below) in sip.conf to be able to support video calls.
videosupport=yes ; enable Asterisk video support