In addition to the growing numbers of liturgical scholas appearing around the country (here is a map), there are also many secular groups that are devoted to excellence in performing the glorious polyphonic music of the renaissance. I just stumbled on Quire in Cleveland, Ohio. What a great sound. It was founded only last year, and it seems to specialize in the English tradition: Byrd and Gibbons mainly but also Ockeghem and Di Lasso.
Here they are singing Sing Joyfully by William Byrd