For a fast food salad, I like both the BTL and the Garden Galley salads at Columbia Harbour House. Here's the BLT salad. I don't have a picture of the Garden Galley Salad.
Raglan Road has a fantastic salad for a lunch entree:
Also POR has a "create your own salad" station. I ordered 2 salads from that station during our trip. It works like a salad bar, only the cm makes the salad for you. The ingredients were good and fresh.
All in all, I've enjoyed every salad (LTT, Hoop Dee Do, Mama Melrose's, Tony's, salads from buffets, etc.--I almost always get a salad for or with a meal) I've had at WDW, with the exception being the appetizer salad at Sci-Fi. I don't have a picture of it, but it was mostly iceburg and the dressing was bland.
If you're looking to eat healthier, keep in mind that many salad dressings are high in fat. You can ask if there is a low or no fat dressing available.
ETA: The chicken ceasar salad at Sunshine Seasons is also a good salad if you're looking for a quick meal in Epcot.