Look Charles there are really many idioms Arabs use for blessing these are some:
حفظک الله و رعاک
hafezak allah wa raak \ i don't know how to write down the pronunciation so you can use Google trans for that.
and it means: God saves you and take care of you.
means: God keeps you in pease
means: God gives you the reward.
جزاک الله خیر الجزاء
jazak allah khair al-jaza
means:God compensates your deed in the best way.
as i said there are many of them and if you are thinking of a specific situation there could be a specific idiom.