The big list
I'm not really a fan of spending an entire column linking items and saying "these are good," so I'm going to leave that part up to you. I've taken the time to compile a nice listing of all available leather armor that comes from reputation and justice points vendors, quest rewards, dungeon bosses, and BoE drops. I purposefully left out the heroic versions of the items to condense the list, so note that every dungeon drop has a heroic version as well that you can upgrade to. If you're an engineer or you know a leatherworker or jewelcrafter, you can also consult this quick list of craftable gear.
For trinkets, there are so many that you are bound to run into two rogue ones eventually. When it comes to weapons, there are also many options, so here's another list of what's available. Note that there's really only one good thrown weapon available, so make sure to pick it up if you can. If you're not able to snag it, there is also a green quest reward from Twilight Highlands that will do. The bonus is that it's one of Garona's old weapons! We want to avoid most guns and bows, since Fan of Knives now requires a thrown weapon to use.
These lists are by no means complete, but they should give you a general idea of where you can get new gear from. You're not going to have "perfect" gear for quite some time; simply replace your weakest pieces first and run dungeons whenever possible. The random dungeon LFD tool is more active than ever, and now is a great time to start acquiring gear for future raids. Make friends with a tank or a healer to make your queues move faster, and just run as many dungeons as you can. There's no reason to focus on a specific dungeon, you'll earn more justice points by running random groups.
As I mentioned above, the new vendors for the Cataclysm reputations have great gear available. If you quest through each of the five new zones, you should be at least honored with each of the five major factions. Ramkahen, based in Uldum, will be an important faction to focus on. They supply us with our helm arcanum, and so we'll want to get revered with them in short order. Similarly, Therezane is the parallel to Wrath's Sons of Hodir, and they're the source of our shoulder enchant items.
Use the new tabards you can acquire from any of the five factions' quartermasters to level up your reputation quickly. Each faction has at least a couple good items for rogues, and so we'll want to eventually level up each reputation as we continue to participate in dungeons.
Reforge trash into treasure
Your first visit to the reforging vendor at level 85 should be to rebalance all of your gear until you can reach the yellow and/or poison hit cap (which is typically 11 percent) and the expertise cap for your character. Reforge your spec's worst stat into hit or expertise rating as needed, and stop once you're there. If you're over somehow, feel free to reforge either rating off your gear until you're back to the caps. Once you have your hit and expertise under control, you can start reforging your worst stat into your best stat. With only haste, critical strike, and mastery available, it's very likely that you'll either be reforging either crit or mastery to haste, depending on your spec.
The key to getting yourself ready to raid is never saying "no" to a gear upgrade. No matter what you do, you're not going to be covered in epic gear without raiding -- there are simply not enough pieces available. Blues are the best you can do, and there are even multiple tiers of good blue gear. By running dungeons and heroics, leveling up strategic reputations, and spending your justice points wisely, you can get yourself kitted out in blues in record time. Blues are find for the starting raids, and if you get to mix in a few epics, you will be more than ready for the challenges that await in the opening tier of Cataclysm raiding.
Check back every Wednesday for the latest strategies in Encrypted Text! Read up on the most popular pre-expansion questions, deep-dives into current class mechanics, and crucial spec and glyph choices for patch 4.0.1! Not sure what your rotation is going to look like at level 85? Read the rotation guide for Cataclysm!