Merriam-Webster's Collegiate Dictionary:
in order that
in order to
in parallel
in part
in partibus infidelium
in particular
in passing
in person
in personam
in petto
in phase
in place
in place of
in play
in pocket
in point of
in praesenti
in principle
in print
in private
in progress
in proportion
in propria persona
in prospect
in re
in reality
in reason
in regard to
in rem
in reserve
in residence
in respect of
in respect to
in retrospect
in return
in reverse
in saecula saeculorum
in season
in secret
in series
in shape
in shirtsleeves
in short
in short order
in sight
in situ
in so many words
in spades
in specie
in spite of
in statu quo
in statu quo ante bellum
in step
in stitches
in stock
in stone
in store
in stride
in substance
in sum
in tandem
in terms of
in the aggregate
in the air
in the bag
in the balance
in the ballpark
in the bargain
in the blink of an eye
in the bud
in the can
in the cards
in the clear
in the clover
in the dark
in the dock
in the end
in the event
in the extreme
in the face of
in the flesh
in the fullness of time
in the grease
in the hole
in the know
in the large
in the light of
in the lurch
in the market
in the name of
in the pink
in the raw
in the round
in the running
in the saddle
in the same boat
in the same breath
