“Ar dhéis Dé go raibh a (h)anam (dílís)” is undoubtedly the most common, widely used even among people with very little Irish.
“Cómhbhrón ó chroi” is
“anam” can be qualified with “dílis” or “uasal”.
“Ní maith liom bhur dtrioblóid”/”Ní maith liom do thrioblóid” is the equivalent of “I’m sorry for your troubles”.
Almost every death in Ireland is marked on http://www.rip.ie, and friends and family members leave condolence messages there, if you want to look for further examples.