My 3 'go to' pasta salads are based loosely around these (they vary depending on what's in the cupboard/fridge)
Pasta, finely diced red onion, black olives, sprinkle of chilli flakes, olive oil, finely diced peppers, diced tomato flesh (seeds, ick), salt, pepper, squirt of lemon juice, (drained)can of Tesco mixed bean salad.
Don't add the onion right away. Put it in a small bowl and soak it in some red wine vinegar whilst your are prepping the rest of it.
*******************************
Pasta, wild garlic green pesto, pine nuts.
*******************************
Pasta, roasted red pepper pesto, finely diced pepper, black olives.