Merriam-Webster's Collegiate Dictionary:
at gunpoint
at hand
at hazard
at heart
at home
at issue
at knifepoint
at large
at last
at law
at least
at leisure
at length
at liberty
at loggerheads
at long last
at love
at most
at no
at once
at one
at one's beck and call
at one's door
at one's elbow
at one's feet
at one's fingertips
at one's leisure
at one's wit's end
at one's wits' end
at peace
at present
at random
at rest
at retail
at risk
at sea
at sign
at sixes and sevens
at speed
at stake
at stud
at swords' points
at that
at the drop of a hat
at the hand of
at the hands of
at the mercy of
at the most
at the ready
at the same time
at the seams
at times
at variance
at will
at work
at worst
at wt
at-
at-home
at-large
atabrine
atacama
atacama desert
atactic
atahuallpa
atahualpa
atalanta
ataman
atamasco lily
atascadero
atat?rk
atavism
atavistic
atavistically
ataxia
ataxia-telangiectasia
ataxic
atbara
atc
atchafalaya
ate
atelectasis
atelier
atemoya
atemporal
atenolol
atf
ath?nai
athabasca
athabasca, lake
athabascan
athabaska
athabaskan
athanasian
athanasian creed
athanasius
athapascan
