Calendaris a one of Gread fucntion while retriveing date from user end , there are lot many use of calendar ex- date of Brith , Order date , Shipping Date and lot many..
in this case selecting proepr date is very imp , in term's of DD/MM/YYYY, some where using YYYY/MM/DD or MM/DD/YYYY , so in this case its its not undustable for the End user to Write Proper date in Text Box , but if you use Drop down in term of (DD/MM/YY or MM/DD/YY ) then its useful for the user ,
1.Ajax enabled DatePicker v4 :
2. VLA Calendar version 2
3.Customizable calendar component
5. Fancy moo tools date picker
6. Clean Calendar
7. Date picker Widget
8. Yet another JQuery Calendar
hope this collection likes you.