Each Primary profession gives certain advantages unique to practitioners of that profession. The crafting profession bonuses, by design, are all roughly comparable.
Epic Engineering Helms can be socketed now with Engineering only gems. They called Cogwheel, and you can see the full list of Cogwheels here. These will allow you to customize your stats even more. Engineering helms are really good right now for the first raid tier. I don't know if they will update these with new raid tiers like once they did in the Burning Crusade expansion.
- [Lifeblood] - 480 haste for 20 seconds, 2 minuntes CD.
- [Felfire Inscription] 130 Intellect, 25 Haste (+80 Intellect over the normal enchants)
- [Inscription of the Earth Prince ] 195 Stamimna, 25 Dodge Dodge Rating (+120 Stamina)
- [Lionsmane Inscription ] 130 Strength, 25 Critical strike rating (+80 Strength)
- [Swiftsteel Inscription] 130 Agility, 25 Mastery (+80 Agility)
- There is a Jewelcrafter only gem called:[Chimera's Eye]. It gives +27 stats over the normal gems (or +41 stamina). You can only use 3 of these on your gear. (+81 stat, +123 stamina)
- Leatherworking 80 Agility, Strength, Intellect or 152 Stamina, because there is no new Cataclysm Stamina enchant yet.
- [Thougness] - 120 Stamina
- [Master of Anatomy] - 80 Critical strike rating
It's not really and eng-game bonus, but currently if you are lucky enough to get the epic items with Archaeology, some of them are better (or almost the same) than the first raid tier weapons/armors. Unfortunately as I mentioned in my Archaeology guide, it takes a lot of time to level this profession and the epic items starts at skill 450, which takes about 20 hours to reach and then then it's all based on luck. Some players got [Zin'rokh, Destroyer of Worlds] as their first artifact after 450, others are solved almost everything and still wasn't lucky enough to get that weapon.