The Libra Eorzea app for iOS or Android, xivdb.com, or the Lodestone Play Guide are all good for looking up info on gear, items, recipes, quests, etc. ffxiv.gamerescape.com has some nice info (like their unlock guide). Eorzeareborn.com has some nice dungeon guides. If you're interested in crafting, then you should check out ffxivcrafting.com (formerly craftingasaservice.com).