With so many options available today, your choice depends on the climatic conditions. Woven wool or woolen blends are the nice choices, predominantly in colder climates. Popular alternatives are viscose, poly, cotton, spandex blends. Once again it's at individuals comfort.
The most popular choice Grey Trousers. You are guaranteed a harmonious outfit, there is absolutely no color or pattern of shirt which clashes with Grey trousers. You can see it goes brilliantly with any jacket, without any compromise with versatility. Well like the navy blazer, these will never go out of style.
Navy blue and Grey are the formal choices.