Useful Links

General Links:

Tolkien Gateway - a wiki, a gallery of images, and much more.
Lord Of The Rings wiki
The Encyclopedia of Arda

Specific Links:

Uncommon and archaic words used by Tolkien
Tolkien Gateway: Pictures
The Book Of Lost Tales - Facebook Page
The History of Middle-Earth Summaries
The Book of Lost Tales, Remade - a fan-written version of the Lost Tales, integrated with the later cosmology and incorporating The Silmarillion.