FTD.com offers same-day delivery starting at $14.99 for a large selection of floral arrangements. Enter the recipient's ZIP code at the top of the page to see what styles are eligible for this delivery option. Choose from cut flowers, Christmas arrangements, plants, and more.
Same-day delivery is available through December 24, although it appears that you must place an order by 2 pm local time. (Note, however, that cutoff times may vary by location.)