What a good question!! I always end up with the same salad. On a red day I do basic lettuce, cherry tomatoes, cucumber, spring onions all chopped up and mixed in a bowl, but getting bored of it now!!
On a green day I do potato salad: boiled new potatoes, peas, grated carrot, boiled pasta, red onion and hellmans extra light mayonaise (0.5 syns per tablespoon) and it's yum!
I like the idea given above of adding tuna. I should use peppers more too, they add a bit of colour.
Cant think of anything else yet, but hopefully there will be a few more ideas.