Evoker

[SirValentine]

So the (Greater) Spell Focus augments stack with spell focus items. What is a spell focus item?
Are you referring to spell penetration items?

What about the (Greater) Spell Focus feats? Do they stack with the augments or spell penetration items?

Spell Penetration is caster level check to overcome Spell Resistance. It only applies to certain spells (does NOT apply to most damaging spells; only a few Druid spells need Spell Penetration), and only to certain mobs (those with Spell Resistance). It is totally separate from your spell Difficulty Class ("DC") which determines how hard it is for enemies to "save" against your spell. Spell Penetration does not "stack" with Spell Focus because they are two different things.

Spell Focus, be it from items, augments, or feats, increase your DC. The items, feats, and augments all stack with each other. Currently, you can get up to 3 from feats (Epic Spell Focus), 2 from an augment, and 5 from an item. Those are all only for a single specific school of magic, such as Evocation. Examples of spell focus items would be The Nether Orb or the Sage's Locket, though there are many such items, and it also drops on random loot.