Leatherworking has some great potential in Cataclysm. From the Leg enchants, entry level 85 capes, to the Mail and leather Epic chests and belts. Even the leveling gear has potential to make some good gold off of. Also if your Leatherworker happens to be a skinner you will find yourself able to make even greater profit while leveling.
First off the Leg enchants. There are two types of leg enchants with each having rare and epic versions respectively. Melee DPS will be most likely using Scorched Leg Armor and Dragonscale Leg Armor. While tanks and some others will be drawn to Twilight Leg Armor and Charscale Leg Armor. People will be using the rare leg armors to level so profit will be a bit tight on these but I would expect people with smaller budgets grabbing these for their first armor set at 85 expecting to replace them at some point. The player with deeper pockets however will want only the best and only the epic armors will do for them. If there is not a vendor trading Heavy Savage Leather for Pristine Hides I would expect these to go for substantial profit. Whats more the Dragon Scale Leg armor is orange at 425 and so if you can get your hands on the mats you can potentially level with this pattern.
Another item set that should prove to be worth crafting for a good amount of time into Cataclysm is the capes. Just like the leg armors leatherworking has the Melee capes both an Agility DPS and a Strength Tank cloak. Unlike the leg armors these require Chaos Orbs. In case you have not read all my other posts Chaos Orbs are BoP. That means you will have to run dungeons to be able to craft these. It also means you will not see as many people in trade who have the mats and want them made. Yes they may look for people with these orbs who are willing to craft for them but if you choose to go this route I would charge a decent fee for both the Orb and your crafting time.
Along the same lines there are the Epic pieces. These belts require 2 chaos orbs and are mail spell, mail melee, leather spell, and leather melee. The chest pieces require 3 chaos orbs and same as the belts there are mail spell, mail melee, leather spell, and leather melee. These will prove to be highly popular among the Gearscore freaks and people in guilds that expect people to be ready to raid ASAP. The first few of each of these will go for insane prices so if you level your leatherworker first I would gather the mats and create as many of these as possible before moving into the leg armors and other armor pieces.
Now another route to take if you can't get hold of Chaos Orbs on your leatherworker is to craft the rare PvP sets. These should prove to be very popular with the new rated BG system which will allow more people to participate in rated PvP and do it at their own pace. Smiler to the Epic peaces their are sets for each. The leather spell set is the Bloodied Wyrmhide set, leather melee is Bloodied Leather, mail spell is Bloodied Scale, and mail melee is Bloodied Dragonscale. I wouldn't expect these to fetch outrageous prices after the first few days but with so many items to craft there is no doubt there is plenty of gold to be made here.
As for leveling gear outside the two cloaks for level 83 the rest of it is a crap shoot. They all have random enchantment associated with them. Also while there are many choices of which patterns to use I believe enough people will be creating these that unless you manage to get one of the more desirable stats you may be wasting your time crafting a lot of these early. Later on when holes are found in gear picked up while leveling some of these pieces will prove profitable, but I wouldn't bother making more than you need to until these holes are found.
Well only Tailoring left... Not quite. After Tailoring I will be making a quick look at enchanting along with the gathering professions. This will bring us to Dec 6th just in time for Cataclysm. I hope you have all your plans for leveling almost complete and if your not ready with buff food and items and such I would start collecting it now so as to not waste any time when you log on Dec 7th. With that I leave you with this question. What is your reason behind the first toon you will level in Cataclysm?