Walla Walla is a town with charm. I like downtown especially, it's cool. I was there for work, but would love to go back for a weekend. I asked a couple locals where the best breakfast is served and they gave me some great suggestions:

Big portions and affordable. "Hole-in-the-wall" in the best sense of the term.
Hometown diner. Try the pumpkin pancakes. The Big Walla Walla Breakfast is recommended. The feathered eggs and biscuits & gravy are popular. Best corned beef hash around. Go early because it fills up.
Good savory items. Try the migas.
Indulges the sweet tooth. Amazing menu. The Traditional breakfast is recommended. Also try the yogurt parfait (light and delicious). I hear the servers are cute and the mimosas are great. Their corned beef hash is also worth a try, as is salmon eggs benedict. Go early because it fills up.

Recommended for coffee and pastries.