Warrior class is an excellent class if you want to make a monster a little bit more of a challenge to your party but dont want to effect its CR too greatly. D10 HD, +1BAB and almost full proficiencies is nice.
want to make a minotaur just a bit harder without a massive CR change? give him 1 lvl of warrior, throw a breastplate on it and adjust its HP and BAB/attacks accordingly.
warrior/adept is also very good for very low level town npc's. town guards, temple servants, priests, thugs etc etc.