These are resources that I’ve personally found useful for learning about fountain pens, ink, nibs, paper, etc. I’ll add more to this list as I come across new sources.
Goulet Pens’ Fountain Pen 101 series
Rachel De La Fuente’s Fountain Pen 101 series
Rachel De La Fuente’s Fountain Pen 201 series
Anderson Pens’ ink comparison tool
Sailor Pens nib sizes info
Nib tipping sizes
Richard Binder’s Glossopedia of Pen Terms
Pen Show Listings
Info You May Already Know
Fountain Pen Day is celebrated the first Friday of November.