The most beautiful part of being a linux user is the choice you have, whatever issue it is. Like any other Linux distro, Ubuntu is infinitely customisable with any number of themes and applications. This include login window themes or gdm themes as well. More here
And i think may be that is the problem. I am not saying it as a bad thing but still, you are simply overwhelmed by the sheer number of choice you have. Here is select set of login window themes that i think are really worth a look.