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I've picked out some options for each slot that you may want to track down for your own use. I've focused mostly on gear that is relevant to level 90 characters getting ready to raid, so I'm not looking at drops from normal mode Temple of the Jade Serpent, for instance. Know that some are locked beind rep grinds or will be ludicrously expensive for several months, so plan accordingly. I'm also including Brewfest drops since it will be active as most of us are still leveling and gearing. I should note that this isn't a complete list since a lot of items on Wowhead's database have little to no information about how to go about getting them.
Yup, it's a boring gear list. If you're trying to gear up and raid on the first week, just grab what you come across rather than trying to focus on building a "best in slot" set. Knowing what is "best" is helpful, but with the RNG of drop rates and the fact that rep grinds will always take a certain amount of time, it's unrealistic to expect that you'll be able to get all (or even most) of it in the short time you have. Go for what's in front of you and try for the better stuff when you have time.