Bladedancer / Swordsinger
Hawkeye / Phantom Ranger / Silver Ranger
Treasuer Hunter / Abyss Walker / Plains Walker
Elementar Summoner / Warlock / Phantom Summoner
Dark Avenger / Paladin / Shilien Knight / Temple Knight
Spellsinger / Spellhowler / Sorcerer
Moreover nobody can sub the classes Overlord and Warsmith, they can only be played as main class.

Kamael race can only sub Kamael classes and the last subclass will be Inspector (not as main class available).

Nobless / Olympiad / Hero:

When your first subclass becomes level 75 you can become Nobless (the quests can be started earlier). A Nobless character has a few advantages. They can port to places which aren`t available for other players, they can summon cp potions (restore combat points; kind of hp only for pvps), they got a buff called Bless of Nobless (you don`t lose your buffs when you die, it lasts 1h) and you can participate in the Olympiad Games.

The Olympiad Games are a tournament where the best player of each class is ascertained. This player becomes Hero! :D

The hero gets a special weapon, a glow and he can use a world shout.

Hm so this is it for now, propably I forgot something important or nice feartures. :D

PS.: Yeah I know some classes in Lineage 2 Adena aren`t that great to play, but if you know how to play those "sucky" classes you can kill many players. For example in c3 the Gladiator was a so called gimp. True he was weak, but still I know some Galdi players that kicked the asses of many omfgpwner classes. :D