One popular site for unique and personalized gifts is http://www.zazzle.com/ and for their Famed Prints and KEDS Custom Shoes, the deadline has come and gone. For others, it's tomorrow for the most economical type of shipping. Expidited shipping is available as late as 5/5, but it comes with a price. Order by 6 PM pm april 21 to avoid paying extra to get your selections delivered on time.
Click on the MOTHER'S DAY SHIPPING INFO link in the upper right hand portion of the main Zazzle page for a complete schedule. April 21 6 pm (Pacific Time) is the deadline for most products to be shipped economy and still arrive on time.
Zazzle is just one example, and they have a reputation for meeting or beating their deadlines pretty consistently. Check your own favorite website for their shipping schedule, but do it now, as it's awfully easy to get caught in the lurch!