willow and bamboo depending on the variety can be fast growing and be useable in just acouple of years. check the second link for fast growing oaks.

http://www.bowhayestrees.co.uk/willows1.htm

http://www.fast-growing-trees.com/

maybe think about planting herbs plants and trees that have medical uses like Eucalyptus.

http://www.gardensablaze.com/HerbEucalyptusMed.htm