I've been experimenting with different non-fat, low-cal dressings. There's a brand called "Maple Farms" or something like that (I'm in the U.S.), and they have several good options. Their balsamic only has 5 calories for 2 Tbs, and they have several others that aren't a bunch worse.

I've also tried hummus on salad, and I might try salsa, too. It doesn't take a lot to flavor a salad if you toss it really well, thankfully.