There's lotsa good stuff you can put in them. Some people like to put seeds or nuts, my dad puts sunflower seeds in his and at school they offer flax seeds at the salad bar. Supposedly they're really good for you and I like the crunch, but seeds and nuts have lots of oil so don't put too many or you'll up the calories more than you'd like, probably :P
There are also lots of different cheeses you can put in, cheddar and feta are two of my favorites. Once again don't overdo those, a little bit goes a long way. You can try different lettuces or spinach instead of plain old iceberg or romaine. Some lettuces are bitter and add some complexity to the salad, if you're into that sort of thing.
As for vegetables, in addition to what you listed, I also like mushrooms, carrots (you can shred them if you want), raw broccoli, string beans, bell peppers, things like that.
As for salad dressing there are tons of lighter options out there for about the same caloric intake you'll get with plain old oil and vinegar. Italian and cesar are two of my favorites. Also, if you want to make your salad more "meal like" you can add some lean protein like chicken or a whole hard boiled egg and that will keep you a bit fuller. Eggs are fairly cheap and you can hardboil a whole bunch at once, they're great for snacks on their own as well.
Salads are great, I have one before dinner on days that I want to eat less and they keep me full so I don't snack late at night. I hope you keep eating them!