Hi,
So far, just simple and quick stuff: upper grill block, cover the foglight/fake brake cooling intakes, seal the hood gap with foam gasket, and a bit of homemade zigzag tape on the front of the hood and at the top of the windshield.
We got the best stock wheel covers (I hope to put on some smooth ones from Hubcap Mike's), and so far it has always been better than EPA combined. My spouse needs to get some more practice ecodriving; as I manage to better her mileage by 4-5mpg.