I eat a lot of plain yogurt (GO diet encourages it...) so I was also racking my brains trying to figure out how to make it peppier. I came up with the following two options (hopefully they will work for you):

Adding vanilla extract and Splenda (I've found 3 tsps of the loose powder Splenda, not packets, is more than enough and I believe it's only 1 carb) for a natural vanilla taste.

Adding sugar free maple syrup. I recently discovered Maple Grove Farms/Cozy Cottage (it goes under both names) has one they make with Splenda and it's awsome. Very natural tasting (to me at least) although pretty wattery. I think it's 1 carb per tablespoon. I got it at Albertsons so I think it's readily available. I like my yogurt/cottage cheese sweet, so I add more Splenda on top of it, but usually just a teaspoon. The syrup does have a nice maple flavor.

Hope that helps!

Tam