Anybody know a good CSS minifier?

I'm looking for something that can concatenate selectors into comma separated lists.

For example:

.a{
    display:none;
}
.one{
    font-size:20px;
}
.b{
    display:none;
}
.two{
    font-size:20px;
}
.c{
    display:none;
}

will become:

.a,.b,.c{
    display:none;
}
.one.two{
    font-size:20px;
}

I've seen minifiers that will combine blocks that are next to each other but I want one that will combine anything with identicle atributes.

Cheers,
Mark