There are 2 options (on applications which havn't overridden default key bindings) -

a) cmd-left arrow for beginning and cmd-right arrow for end of the line.

b)emacs key bindings are available as well control-a and control-e for the beginning and end of a line.

Option a) gets slightly complicated in text entry on edit controls of browsers which have the cmd-left arrow key mapped to previous page (Firefox). In addition, a lot of multiplatform software ends up making things behave like on Windows ( Microsoft Office being one) by overriding defaults for these keys and home and end keys do take you to the beginning and end of the line there.