Here are a few:
St. Irenaeus—fought against Gnosticism
St. Francis de Sales—instrumental in turning 72,000 Calvinists back to Catholicism
St. Charles Borromeo—implemented the decrees of the Council of Trent
St. Teresa of Ávila—reformer of the Carmelites
Reform Yourself!: How to Pray, Find Peace, and Grow in Faith with the Saints of the Counter-Reformation.