This is my favorite flower shop in Ithaca. it is a bit out of the way and would require a car to get to, so it isn't too convenient for many students, but the flowers there are spectacular.
I have gone there on many occasions, but mostly on Valentine's Day. They have a great assortment and you can call ahead and reserve either a single rose or a whole bouquet. While prices everywhere are grossly inflated on Valentine's Day, I found the prices at Michaleen's to be pretty fair.
They have a nice selection of different arrangements and they also have other gift items like balloons and candy.
If you are willing to drive a little bit, this is the best florist in Ithaca if you ask me.