Usually for those situations I just try to pick something that's a little more unique (maybe __bar_args). For things that end up defining globals I've used this technique before:

    #define CAT2(a,b) a##b
    #define CAT(a,b) CAT2(a,b)
    #define Unique(symbol) CAT(symbol, __LINE__)

and then use

    #define my_useless_macro(value) \
        static int Unique(__macro_var_name) = value

…with the (large?) caveat that it won't work if you put 2 on the same line:

    my_useless_macro(0); // works
    my_useless_macro(1); my_useless_macro(2); // Fails

If you expect to call my_usless_macro() multiple times on a line (hint, macro expansions are always on the same line), then you might put an extra optional parameter in there with __VA_ARGS__, like this:

    #define my_useless_macro2(value,...) \
        static int Unique(CAT(__macro_var_name, __VA_ARGS__)) = value

and then this will work:

    my_useless_macro2(1,a); my_useless_macro2(2,b); // works
    #define doubly_useless(a,b)    \
        my_useless_macro2(a, __1); \
        my_useless_macro2(b, __2)
    doubly_useless(3,4);

The C preprocessor is a bit of big hacky mess, but you can do some fairly powerful (and often type safe) things with it.

The magic __COUNTER__ macro supported by some compilers can be used to simulate gensym.