Shadowfax - In the dark, send a message for the fastest bearer.
Huan - Only the greatest can slay the steadfast, if you replace half his ring with another article.
Asfaloth - From Goldilocks to the evening he rides on.
Roac - Black bird croaks with its head and tail cut off.
P - His catlike tread fills us with dread, forgiveness unfulfilled.
E - In the storm, the king's kings are named only for the king.
Arod - One staff given to two friends.
Roheryn - The King rode her in - but never say die!
S - Stubby, slow, and not happy enough to go.
#2: 'Only the greatest [wolf] can slay' is a straight clue. If you take half of 'ring' (ie, the 'ri') from Hurin, and replace it with the article 'a', you get Huan.
#3: 'Ride on' is apparently the translation of
Noro lim, so 'he rides on' is the straight clue. Goldilocks is a translation of Glorfindel. As to whether Arwen's in this one... uh, do I have the right to remain silent?
The remaining three come from three different books, so that's fun.
hS