I suggest that we make a list of grammar reference books
Стеблин-Каменский. Древнеисландский язык.
A comprehensive grammar reference in Russian. It can be googled for.
A. Heusler. Altisländisches Elementarbuch (archive)
A. Noreen. Altisländische und altnorwegische Grammatik (archive)
Phonetics, morphology
M. Nygaard. Norrøn syntax (archive)
For those lucky ones who understand Danish.
R. Rask. A grammar of the Icelandic or Old Norse tongue
An elementary grammar of the Old Norse or Icelandic language George Bayldon
These can be found at Google Books and seem to be outdated