it's a tough one - can't really think of what hasn't already been done elsewhere several times over.
i've tried a few of these quick launcher and replacement menu type things but have found you can customise the xp task bar enough to do most of what these extra utils do.
one thing springs to mind that i don't think i've seen functional elsewhere; the ability to drag and drop a file onto one of the program shortcuts contained in the quick launcher bar, thereby opening the program up with the file open and ready for action inside it - just as you can do with your normal icons scattered around your system. stick a recycle bin button on it and this could work like a floating bin - drag the file(s) onto it to delete and 'scrunch', gone.
another nice feature might be something that would provide buttons for common tasks. say, a button to create a new folder on the desktop (i know right click and all that - sorry, it's too much for me).