I also think lilies give quite of bit of bang for the buck. If you change the water every few days and cut the stem an inch, lilies can last up to 2 weeks. The lower blooms fading while the upper buds begin to open.
And the scent! The minute we open the front door, the heady scent just wakes up the senses. I like to put single stems in vintage decanters and apothecary jars, so you really get to focus on the beauty of the flower. The hefty weight of the vessel also helps the lily from falling over.