How to monitor file access for an OS X application? I am looking for the OS X corespondent of FileMon, that was later included in ProcessMon.

BTW, it is essential to be able to filter by process.
Instruments—a part of the Apple Xcode development suite—can monitor all file access and writes. Open it from /Applications/Xcode.app/Contents/Applications/Instruments.app, select your application or process, and press Start. You have extensive filter options available in the menus.

Older versions of Xcode are storing the App at /Developer/Applications/Instruments.app