Birch dowels or chinese privet shoots. I'd make arrows out of ipe too if it didn't take so darn long. Those are my favorites.
*Edit* That didn't make much sense.
Birch and privet are my favorites. They are very light in color (which gives me a wide range of shades if I decide to stain them), are relatively easy to straighten, and resemble red osier and yaupon holly respectively (which is great for reproductions).
I've made ipe foreshafts (and arrowheads) and it would be great for arrow shafting if it wasn't so hard on my tools.