I've searched for ravens throughout most of JRRT's works (including the HoMe; not searched VT and PE, though). IMO, there's not much more to add. Perhaps something could be said about their association with "darkness" (as in the colour black), which appear in not so few places. See e.g.:
 Inspiration from Norse mythology
An observation from the research: In The Legend of Sigurd and Gudrún appears a pairing of wolves and ravens:
This pairing is echoed in The Lay of Leithian:
- I think this is a brilliantly useful and insightful observation, which must be included! And, of course, in English literature ravens are frequently associated with ill-omen (most famously in Edgar Allan Poe's "The Raven").
- In the UK, the government makes sure that there is a minimum of six ravens at the Tower of London (including clipping their wings and having "reserve" ravens) as there is a belief that if the ravens leave the monarchy will fall. Perhaps the ravens of Erebor are performing a similar function to the ravens of the Tower of London? --Mith (Talk/Contribs/Edits) 13:08, 5 December 2010 (UTC)