I'm admittedly not a huge Disney fan, but I'd have to say Tiana from Princess and the Frog. She is my favorite Disney Princess, and I admire her work ethic.
I love that she keeps herself motivated enough to work through a sucky, dead-end job until she can save up enough to reach her grandest aspirations. She is passionate and she is persistent. She has been at a disadvantage by being a woman from a lower-income community in a time that was hardly accommodating, but she never even thought twice about it. And I know that even if she hadn't found her Prince, she would've kept working until she achieved what her heart most desired. Sometimes I think about that when I'm feeling like I can't go any further.
Oh, and I also just kinda want to be a frog sometimes.