Oops - bards need high CHA, too
Most monsters are too stupid/ugly/foolish to be any spellcasting class (most are relegated to being fighters, barbarians, rogues, or... rangers (for some reason)). Plus, monsters cannot have deities, so you cannot have clerics, either.
Still, I found that goblins make interesting druids, and some of the bugbears around can be spellcasters as well; there are more as well (more difficult monsters tend to have better stats).