@Quaziz: If you mean 2 poke combos, then gyarados + electrivire and tangrowth + heatran are the most famous ones. If you mean defensive walls, then gliscor, weezing, cresselia and dusknoir are good examples. Be careful how you use both of these in teambuilding though; you can't just slap together the three "combos" and have a good team. Similarly, make sure that the walls fit in well with the rest of your team before adding them.