I've been using a set of the standard Northwind flags for a couple of years now; they're made by Richard Storms out of Deadwood, SD. The units seem to very well made and the flags are very sensitive, reacting to wind speeds well under a couple of winds per hour. The nice part about these flags is that each one comes with its own stand. If I remember the stands are metal sheet music stands with fold-up tripod legs, that telescope up and down, so the entire stand can be made very compact.
So far, I've been very satisfied with mine. I used home-made flags for many years but wished I had gotten good flags when I first started using them more than 20 years ago. Here in the windy Big Sky country, I can't imagine trying to seriously develop accurate loads without at least one decent wind flag!