I agree strongly with the books already mentioned at the bottom of the learn page however the following have merit too for particular topics or techniques
Brainerd WS, 2015 Guide to Fortran 2008 Programming, 1st Edn, London, Springer-Verlag
Numrich RW, 2018, Parallel Programming with Co-Arrays, 1st Edn, Boca Ratan, CRC Press
Akin E, 2003, Object-Orientated Programming Via Fortran 90/95,1st Edn, Cambridge, CUP
McCormack D., 2009, Scientific Software Development with Fortran, 1st Edn, Marston Gate, Amazon.co.uk
A related suggestion… would a book review page be appropriate, even just as a guide to people who want a particular book on a particular aspect or Modern Fortran?