Some handy .hgignore expressions:

Ignore .DS_Store and ._* files:

(^|/)\._[^/]+$
(^|/)\.DS_Store$

These expressions exclude the directories build, dist and nbproject/private. Depending on your project setup, you may want to also exclude bin, gen, nbbuild or the complete nbproject directory.

Only in the top directory, but not in subdirectories:

^build$
^dist$
^nbproject/private$

Only in the second level directory, but not in subdirectories:

^[^/]+/build$
^[^/]+/dist$
^[^/]+/nbproject/private$

In any direcotry:

(^|/)build$
(^|/)dist$
(^|/)nbproject/private$

If you don't want to check in the Eclipse project, but only the sources, yut add:

^.classpath$
^.project$

Version Control System produce backup files when doing irreversible changes.

\.orig$
\.orig\..*$
\.chg\..*$
\.rej$
\.conflict\~$