Zombie Lord and Skeletal Champion are exactly what you are looking for.
Zombie lords are the fleshy counterparts of skeletal champions—intelligent, cunning, and envious of creatures whose bodies aren't rotting away. Despite their decaying flesh, they are not slow like common zombies, and can easily pursue fleeing prey. Zombie lords are more powerful than common zombies and retain their class levels.
These templates transform any living intelligent creature into an undead, just like regular Zombie and Skeleton do. But the creature keeps all class levels complete with class features, HD, skills and whatnot. And nothing prevents them from gaining more class levels, too.
Apart from Constitution becoming a non-ability (Con --) due to the undead type, the ability scores aren't touched at all. Most importantly (and different compared to regular Zombie/Skeleton), Intelligence remains untouched. Speech is not actually spelled out, but neither is it for Vampires.
There's an example Human Zombie Lord Monk on the SRD. He has all class features of a 3rd level monk, along with skills and languages.