Pastoral - Beethoven's 6th Symphony (my favorite) and Bach's Sheep May Safely Graze are both in the key of F. Carl Haas mentioned that that key was used for several "pastoral" pieces and had a "pastoral" flavor to it.

Slow Airs - Musicman's CD Farewell has beautiful Celtic waltzes and slow airs. I'd love to hear of other ones, especially the Scottish ones.