Both American and Continental arrive at the same terminal in Cabo (San Jose del Cabo to be exact) and that is terminal one.
Since I always arrive on Alaska Airlines at terminal three, I don't know the exact set-up of the other terminals. But, if it's anything like terminal three you'll go through customs first, retrieve your luggage at baggage claim, and then exit. The car rental desks are by baggage claim in terminal three so if that's the set-up in the other teminal that would be a convenient place to meet. It's not a huge terminal so I would imagine if you are standing by ANY car rental desk you'll find each other. I think there is an Avis desk, though.