Spirits:
Selfless Spirit
Anafenza, Kin-Tree Spirit
Eidolon of Rhetoric
Kami of False Hope
Kataki, War's Wage
Bygone Bishop
Most of the white spirits are sideboard cards, with specific uses against certain decks. Selfless Spirit and Anafenza, Kin-Tree Spirit are the only cards I would consider using, with Anafenza being only a one-of at most, and Selfless Spirit being a four-of cornerstone of the deck. The sideboard spirits, however, are more interesting. Eidolon of Rhetoric is a great card against Storm, ad nauseum, and other decks looking to cast at more than one spell per turn, or combo off using spells, Kataki, War's Wage hoses affinity, and
Kami of False Hope
is a mediocre sideboard card, only usable in the narrowest of circumstances. I probably would not play Bygone Bishop, as it is Lightning Bolt-able, and dies very easily without netting you a clue.
Non-Spirits:
Thalia, Guardian of Thraben
Thalia, Heretic Cathar
Aven Mindcensor
Normally, I would not put these non-spirit cards in a Bant Spirits list. I have seen some people run 1-3 Thalia, Guardian of Thraben in the main. Thalia, Guardian of Thraben is a sideboard card that some people use, as it is very annoying against Storm, Burn, ad nauseum, and other Blue control decks. Thalia, Heretic Cathar is good against decks with lots of Fetchlands, and Can be helpful in beating company decks with lots of creatures to block yours. It and Aven Mindcensor are both fringe sideboard cards that are rarely seen.