That all depends on the type of plasma you intend to get.

If it has all the connections and receiver cards built in then you need to think about 4 or 5 mini coax feeds for component and composite video feeds and definately a HDMI lead.

Others will include a standard coax for TV and Freeview and possibly a pair of phonos for audio (if you are having speakers on the plasma)

The alternative is a plasma that has its own media centre type box which sits remote to the screen, connected by an proprietory (spelling) cable and connector. The Media box receives all the incoming signals and sends the chosen one to the screen. WATCH OUT these 'special' leads can be expenceive to by longer lenghts.