I just realized I'd never actually drawn Twilight Sparkle before. This seemed... wrong. THERE I FIXED IT.
This is wallpaper-sized (for me) at 1280x800, but it's at 400dpi, so it should size up very easily to most screens. ^^
(And yes, it's oriented for a desktop that has icons along the right side instead of the left. I'm a Mac user. If it bothers you, then flip horizontal is your friend.)
Oh, and that subtle cloud in the background is a delectable graphic I ganked from Boxdrink: [link]