If you're interesting in generic fun sailing and don't plan to race, you can't beat calling Rudy at D&R. They carry Daysailer-specific gear including sails.
http://www.drmarine.com/products.asp?cat=124
If you're thinking of racing and want to go with heavier-duty gear, Hank Jotz is often recommended:
http://www.jotzsails.com/dspl.html
you could also go to the "Sails" section under the "Technical Info" menu selection up at the top of this page and find a bunch of other makers that do Daysailer-specific sails:
http://forum.daysailer.org/tech_sails.php
Have fun buying!
Carlos