I tested just about every item you could think of at the Enchanting Altar in Ruins of Naar and these were my results. I will not explain how to enchant an item, because the game already explains that to you nor will I list the amount of each items required for the enchantment, because I'm lazy. However, on average it takes 8-10 of an item to get a buff with a Red Gem. All values here are based on using a Red Gem so obviously a lesser stone will yield lesser buffs:

Blooddrop Cap = +4 Strength
Falconskrye = +4 Dexterity
Mudwort = +4 Vitality
Etherweed = +4 Willpower
Wormroot = +20 Health
Spices = +20 Energy
Herder Cap = +20 Accuracy
Rock = +12 Protection
Palenut = +12 Evasion
Saltweed = +12% Health Regen
Grimcap = +12% Energy Regen
Bleeding Blossom = +12 to all Resistances
Meat = -16% Food Consumption
Horned Fruit = +12% Experience Gain
Fish = ~90% Weight Reduction


Weapon only enchantments:

Crystal Flower = +8% Critical Chance
Blackmoss = +12% Cooldown Reduction
Copper Nugget = +8 Damage

In the South Westernmost area of Crystal Lake there is a book locked behind a Gold Key that will give you a skill called "Professional Enchanter". It's not as amazing as I thought it would be, but it does add +1 to every buff you apply to an item. So theoretically if you were min-maxing a character and wanted to buff all 10 items they carry that would make a big difference. It seems a little lackluster for 1 Gold Key, but if you're going to do a lot of enchanting then it's a must have.