Favorite substitutes?

What are yours?  Mine include spaghetti squash in place of noodles - I don't feel so bad about the meat sauce and a little garlic bread with this, though I don't indulge in it too often.

I'm sometimes picky with dressings, so sometimes I use no-sugar-added applesauce over lettuce, tomatoes, carrots, etc. Doesn't work so well if also have croutons, but makes a tasty fruit-veggie combo in my book. Applesauce is also a great swap for oil in some baking recipes.

Do you have any favorite swaps and if so, what?

And still looking for a great butter substitute - suggestions?