Noel,

A natural choice would be some type of evergreen. Aborvitaes are nice but they don't always "fill out" if they are grown too tall. This can be avoided with pruning/shaping. Also spacing is a consideration. Hemlocks are fast growing but have the same considerations as the arborvitae. Privet hedge is an excellent choice! Individual plants grow together well and solid hedge can be pruned into a number of nice shapes. Never had a problem with mosquitos(Here in the Northeast), but bees once and a while seemed to enjoy building nests in them. Holly plants are beautiful but I don't know if they can be turned into a single hedge. If you decide on the holly make sure to get male and female plants so you can get the brilliant red berries(DON'T let the kids eat them). Juniper can also be grown into a hedge, as can yew though it probably won't be the height you want. Good Luck!

George