Recommended gcc warning options for C [closed]

Other than -Wall what other warnings have people found useful?

http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Warning-Options.html

I routinely use:

    gcc -m64 -std=c99 -pedantic -Wall -Wshadow -Wpointer-arith -Wcast-qual \
        -Wstrict-prototypes -Wmissing-prototypes

This set catches a lot for people unused to it (people whose code I get to compile with those flags for the first time); it seldom gives me a problem (though -Wcast-qual is occasionally a nuisance).

As of 2011-09-01, with gcc version 4.6.1

My current "development" alias

gcc -std=c89 -pedantic -Wall \
    -Wno-missing-braces -Wextra -Wno-missing-field-initializers -Wformat=2 \
    -Wswitch-default -Wswitch-enum -Wcast-align -Wpointer-arith \
    -Wbad-function-cast -Wstrict-overflow=5 -Wstrict-prototypes -Winline \
    -Wundef -Wnested-externs -Wcast-qual -Wshadow -Wunreachable-code \
    -Wlogical-op -Wfloat-equal -Wstrict-aliasing=2 -Wredundant-decls \
    -Wold-style-definition -Werror \
    -ggdb3 \
    -O0 \
    -fno-omit-frame-pointer -ffloat-store -fno-common -fstrict-aliasing \
    -lm

The "release" alias

gcc -std=c89 -pedantic -O3 -DNDEBUG -flto -lm

As of 2009-11-03

"development" alias

gcc -Wall -Wextra -Wformat=2 -Wswitch-default -Wcast-align -Wpointer-arith \
    -Wbad-function-cast -Wstrict-prototypes -Winline -Wundef -Wnested-externs \
    -Wcast-qual -Wshadow -Wwrite-strings -Wconversion -Wunreachable-code \
    -Wstrict-aliasing=2 -ffloat-store -fno-common -fstrict-aliasing \
    -lm -std=c89 -pedantic -O0 -ggdb3 -pg --coverage

"release" alias

gcc -lm -std=c89 -pedantic -O3 -DNDEBUG --combine -fwhole-program -funroll-loops

I started out with C++, so when I made the switch to learning C I made sure to be extra-anal:

-fmessage-length=0
-ansi -pedantic -std=c99
-Werror
-Wall
-Wextra
-Wwrite-strings
-Winit-self
-Wcast-align
-Wcast-qual
-Wpointer-arith
-Wstrict-aliasing
-Wformat=2
-Wmissing-declarations
-Wmissing-include-dirs
-Wno-unused-parameter
-Wuninitialized
-Wold-style-definition
-Wstrict-prototypes
-Wmissing-prototypes

I like -Werror. Keeps the code warning free.

Get the manual for the GCC version you use, find all warning options available, and then deactivate only those for which you have a compelling reason to do so. (For example, non-modifiable third-party headers that would give you lots of warnings otherwise.) Document those reasons. (In the Makefile or wherever you set those options.) Review the settings at regular intervalls, and whenever you upgrade your compiler.

The compiler is your friend. Warnings are your friend. Give the compiler as much chance to tell you of potential problems as possible.