Hey Hey Hey :D
Long dresses are a signature from our idol Taylor Swift. So if you want to pick a Long Prom Dress, let's focus our attention on her Fearless Tour.
I will give you some inspiring dresses similar to that one she wore during her live performance of Love Story, on her Fearless Tour!
#1 - Floating White Dress
Even without those shinning sparks that Taylor loves to wear (on the top) I think this one is the more floating one, and cinted one, and I SIMPLY ADORE THIS ONE! (link here) !
#2 - Sparkling on Top Floating Dress

This one has rhinestones, if you loved this one, check it out, here !
#3 Rhinestones cinted dress
Super long and shining on top, it will blind someone at night ahaha
Get ready for that prom night, you will be "Spinning like a girl in a brand new dress"
Purple was her favorite color, after white! And it also inspired her third album, Speak Now.
Now inspired in her dress wore at her live performance of Love Story at the 2008 CMA Awards, here's some purple long prom dresses to give you extra inspiration for your prom night!
#1 V-neck purple dress
This one is so pretty and has sparkles all around the top! Such a Swiftie thing, right?
(get it here)
#2 Rhinestones girdled dress, strapless - more like the one she wore but with handles...

(this one is available here)
#3 Sparkling dress, not on top, but all over it, sooooo pretty ! Perfect to dance all night, and glow in the dark, you will still light up in the dark, because of its sparks !!
Even the back is so perfect!
(it is available here)
Oh and about purple being her favorite color, Well, Taylor Swift loves all colors but her favorite color is purple!- she said it in the Ellen Show.But i think I have read somewhere that, before that, her favorite color were white :) Here you have a post with long prom dresses based on your idol's favorite colors !