If not too big probably 'Green Giant' arborvitae.

if you were to provide any information about the project.. you might get more suggestions... like:

soil
sun available
height
width
size of yard ...
snow load issues...

etc... etc ...

a 300 foot tall redwood [though zone NOt for your zone] .. will fit the facts you provide ....

as will a 4 foot arb... depending on the circ's of your yard ...

but do understand.. that things conifers/trees never really stop growing ... and many get really.. really big ... so something that grows really fast to the height you need.. will grow right past that size and might get way too big.. way to fast in a small yard .... also.. there is a tendency for fast growing stuff to become very problematic in a fast time ...

if you have a yard that is postage stamp sized .. you might not want something as aggressive as one who has 5 acres might .... now there is an A+ sentence.. lol ..

ken

If you have full sun and a well-drained yard, there should be several conifer choices that would work. Eastern Red Cedar is one that is suitable for almost anywhere east of Mississippi River. Usually has cone to pyramid shape, looks good, and survives with little care. Grows about 24-30" per year down here with watering for first few years. Not sure of rate where you are. It is a native species.

Abies balsamea would be attractive and also different.

Dax

Scratch that. Too slow. Link Below
Picea omorika would be my first choice I think. It grows great in Illinois. Would make a wonderful screen. I purchase my seedlings from Treehaven Evergreen Nursery and here's his Order Form for this year. You can't get better seedlings at any price - anywhere else and his are cheap!

Here is a link that might be useful: Treehaven 2010 Catalog