Released in 1988, Avenir is a geometric sans-serif designed by legendary typeface designer Adrian Frutiger, best known for his Univers and Frutiger designs. Although considered a geometric sans, Avenir has a very humanistic feel to it. Avenir has been a personal favorite font of mine for many years.
If you are looking for an alternative to Avenir, I personally recommend checking out Maison Neue and Adelle Sans. I think Arnhem would make a nice font combination with Avenir.