I was lucky enough to come across a great book called The Tolkien Fan's Medieval Reader. It is a book published by one of the folks on theonering.net, by the name of Turgon. It is a collection of many of the pieces of mythology that had allot of meaning to Tolkien.
The book included things translated from Old English, Middle English, Old Norse, Finnish, Welsh, and Irish.
The main influences i say would be the Old English, Old Norse, and Finnish. In the things translated from Old Norse you find the names Gandalf, Thorin, Gloin, Fili, Kili, etc...
http://www.theonering.net/scrapbook/...ien/view/12722
There's a link abotu the book just so you can see what i'm talking about. The book is quite good. And it will give you a good idea of what influenced Tolkien, and soaked into his vibrant imagination from which he gathered from and began to fasion the fabric of Middle Earth.
Though i must add, to say Tolkien ONLY took old myths and re-worked them would be folly. Tolkien did do that, yet always he was able to add his own twist to the stories, and characters. That's yet another reason i love Midde Earth.
Glofin