Trainer: Adidas Gazelle - light, durable & comfy
early 90's Asics Gel Lytes - same
early 90's Nike Pegasus - saw me through some serious mileage injury free
Flat: Nike Skylon TC (mine have holes in them and I still use them from time to time).
Nike Duelist (5 oz. speedsters, I used these in HS and collegiate track and on dry XC courses)