Level 50-64 items of note. (level 300-375 engineering)
Bombs such as Fel Iron Bomb, Adamantite Grenade, and Cobalt Frag Bomb (which is made at 350 engineering, and already is a WOTLK recipe) will be made while leveling up, but once you've burned through those, and are heading into Outlands, you'll want Saronite Bombs. The Box of Bombs recipe is learned at 405 engineering, but you only need 350 engineering to use them! Look for them in the AH, and buy them when they're a good price, or pay a max level engineer to make some for you.
Goggles are also back in fashion. Now, you could go with Cogspinner Goggles, and hope you get some good stats on the helm. Or you could go for Power Amplification Goggles, which are decent for casters, with no hoping and praying needed. You could wait for level 62 to make and use your class specific helm, but you'll probably be replacing that at level 65 with your cloth/leather/mail/plate version of the Snow Goggles, which usually have pretty nice stats on their random enchants. It's pretty much of a waste of Khorium Bars to make the BC class goggles now, so I don't recommend it. What I DO recommend is the Ultra-Spectropic Detection Goggles, which, while cloth, have a mix of stats that will appeal to any class. Either do the Libram of Constitution quest for more health, or have a level 60 add a Heavy Knothide Armor Kit to your BOE goggles before you equip them. Hint, go for the heavy knothide!! The 10 stamina will multiply with Blessing of Kings, but 100 health won't.
Goblin Engineers will want at least 1 Rocket Launcher, 2 if they're tanks.
Gnomish Engineers would want the Poultryizer, 2 if they're tanks.
Self Portals - Area 52 Ripper for Goblins, Toshley's Teleporter for Gnomish.
Paladin/Warrior Tanks - When you step in Outland dungeons, a Force Reactive Disk on your arm can help you make sure that you stay on top of the threat list, even despite those newly minted DK's doing their best to wipe the run.
Mount - At level 60, you can learn and make your Flying Machine, one of the few profession created flying mounts.
Money Maker - Are you tired of constantly dumping gold into the engineering profession, with nothing to show for it other than being overpowered at your level? The Mote Extractor will start filling your pockets with gold once you hit Zangarmarsh and go thru the quest to learn it. Especially useful in Nagrand for the Windy Clouds, which drop Motes of Air, since Primal Air is usually the most expensive Primal. It continues being useful in Northrend too, with plenty of clouds in Sholozar, Wintergrasp, and other areas to give you free Crystallized elements.
Bubble Belt - Finally, an upgrade for your Gnomish Harm Prevention Belt. The Nigh Invulnerabilty Belt can be equipped at level 50, yet its ilevel is high enough that you could socket it with a belt buckle at level 70.
Xtremely Overpowered Boots - The Xtreme boots for melee toons, and the Xtreme Lite boots for casters. These are yet another engineering item that can accept enchants of a higher level, which would be WOTLK enchants like Icewalker and Greater Fortitude. I know for a fact that they'll take those 2, and they'll probably take Tuskarr's and Greater Assault.