Here are some of the ingredients you could use in a salad bar:
NUTS: Think of all the different nuts there are and how they would make each salad unique... honey roasted peanuts, plain roasted peanuts, sunflower seeds, smoked almonds and candied walnuts are some of my favorites.
GREENS: Greens and lettuces also have many varieties... Romaine, Iceberg, spinach and cabbage come to mind. Each one would add a different twist to your salad bar. You could even have a selection of greens, although I usually only use one type per bar because I want to keep it simple and inexpensive. I like to get the already-cut salads and mixes when they are on sale.
CHEESES: Cheese is a great ingredient for the salad bar. There's Parmesan, Cheddar, Mozzarella, Feta, Blue and many others.
VEGETABLES: There are so many different vegetables and you can even prepare them in different ways for your salad bar, like grill or roast them first or marinate them. Of course the simplest way is to just cut them up fresh! Use your favorites or ones you've never tried on a salad, like asparagus, cauliflower or broccoli.
FRUITS: I love fruit on salads, especially paired with a meat. Bacon and mandarin oranges for example, is one of my favorites. Let's see... ham and pineapple and pork and apple are a couple that come to mind. Don't forget dried fruits. Dried cranberries, pineapple, raisins and many others make great additions to the salad.
DRESSINGS: I usually have a variety of bottled dressings (that I purchase on sale) on hand and occasionally make my own. To cut the calories of the high-calorie creamy dressings, I add vinegar and/or milk to them and to me, they actually taste better thinned out. It also gets on more of your salad being thinner.
SALAD TOPPERS: Even though I could save money and make my own croutons, I like to buy them already-made to save time. I have recently seen other crouton-like items, like flavored tortilla strips made just for salads, but you could always use broken tortilla chips to save money.