Everyone's mentioned stuff I'd have suggested, except for... Jicama! Seriously. We replace half the cabbage in a coleslaw with grated jicama, and om nom nom. It's kind of like cabbage crossed with an apple.

Toasted nuts/and or seeds make any salad awesome. I make my own croutons by tossing homemade bread with melted butter and herbs/garlic, then toasting them in the oven. (I also use them in roast bird stuffings -- mmmm.) Grated carrots add a nice sweetness.

Squeaky cheese? Why have I never added squeaky cheese to a salad? Oh wait -- because I *eat it* before it could be considered as salad stuff.