I can eat these everyday of the week. They're that good. They're pretty basic, but if you want that extra something, I recommend fresh mozzarella, the ripest tomato you can find, and Zingerman's Bakehouse Sourdough bread.
any artisan bread
Preheat panini grill. Lay out bread, spread bottom with pesto sauce, and layer with tomato and mozzarella. Place second bread slice on top of sandwich. Brush both sides of sandwich evenly and generously with olive oil, and grill until cheese is melted and bread is crispy and golden.