Motifs overview

The site Unofficial Elder Scroll Pages has a good overview of all motifs that are currently available and how you can find them.

ESO Sets

The site eso-sets.com contains an overview of all sets in the game (both craftable and non-craftable), where to find them and what their properties are.

ESO Wiki

The The Unofficiel Elder Scrolls Pages is a wiki like site with lots of information about the game.

The Official Elder Scrolls forums

The official forums by Bethesda games and ZOS.