Best GCC warning flags for compiling C++

A recent discussion on ACCU-general gave people an opportunity to share the warning flags they like to use with g++.

I thought I'd write down the consensus as I understood it, mainly for my own reference:

-Wredundant-decls
-Wcast-align
-Wmissing-declarations
-Wmissing-include-dirs
-Wswitch-enum
-Wswitch-default
-Wextra
-Wall
-Werror
-Winvalid-pch
-Wredundant-decls
-Wmissing-prototypes
-Wformat=2
-Wmissing-format-attribute
-Wformat-nonliteral

We were advised by Jonathan Wakely that -Weffc++ is not very useful since it is mostly based on the first edition of the book Effective C++, many of whose recommendations were improved in the second edition, and also apparently GCC doesn't do a great job of warning about them.

Update: thanks to an article[1] by Roger Orr in CVu these flags are highly recommended in GCC 5.2+:

-flto
-Wodr

[1] Orr, Roger "One Definition Rule", in CVu Volume 27, Issue 5 p16 (editor: Steve Love)