1) Archangels - I remember several times having around 40 Paladins, and a banshee would reduce their number to 16, and then an archangel would bring it back to 40. =) And they look great and are powerful.
2) Liches - they have a beautiful, cold, dead face. They are dangerous, with an area-of-effect attack...
3) Black Dragons - if you have at least 20 of them, and you attack...
4) Demonesses - how beautiful and strong they are.
But the most important thing for me:
5) Archdevils in alliance with Dungeon Lords. The complete opposite of Archangels, with their unique beauty. The ability is just great.