Whole Wheat Pasta in place of plain white pasta. I made some this past week for the first time and it was very good! And, it was only about 50 cents more than the regular white pasta. It had just a little bit chewier texture but tasted pretty much the same. My son looked at it funny, noticing that the color was darker. It reminded me of the way lo mein noodles look at the Chinese buffet, so I just told him that's the kind they use at Chinese restaurants and he was more than satisfied with that answer and ate it right up.
Plain Yogurt in place of sour cream. Actually, subbing it 100% for sour cream still doesn't cut it for me, so I've been mixing it about half and half with light sour cream and no one can tell the difference. It works wonderfully well this way in dips and on top of anything Mexican.
Almond Butter in place of peanut butter. I bought a big bag of almonds last week and I found a recipe for almond butter. It was delicious! It definitely wasn't as spreadable as peanut butter but the flavor was great and it was a nice change. It was yummy on bread with jelly and we dipped apples in it too. Here's a pic of my batch.