Wagner

Arguably the most significant composer in the advancement of the brass' importance in the orchestra and the sophistication of the writing was Richard Wagner.  His operas (Ring Cycle) and other symphonic works made significant and frequent use of brass instruments.  Much of his work remains prominent in the brass world for the excerpts and historical application. 

One of my favorite albums of Wagner's compositions comes from the German Brass, in their 2013 album Celebrating Wagner.  

A favorite of so many brass groups for arranging is Elsa's Procession to the Cathedral from Lohengrin (and NOT, as questioned by anyone born this century, from the movie Frozen :-) )  I had the privilege of performing this trombone choir arrangement while at Florida State University in 2013, arranged by Wesley Hanson.