I like Mary-Kate as a first name with Alexander, probably because Mary-Kate ends with that definitive T-sound, whereas Jessica and Christina both end with an A that blends with the A of Alexander.
My two favorite combinations, of the ones you mention, are Mary-Kate Danielle and Mary-Kate Allegra.
(I don't think Allegra is too long. In fact, I think the rhythm of Allegra sounds really nice in the middle. I would worry a little about Allegra blending with Alexander, though.)
Last edited by Nancy C.; 01/10/10 03:56 AM.