1. Using JQuery's DatePicker
2. Using it in Master Page, Content Page situations
To use JQuery's DatePicker, you should have access to JQuery and JQuery UI libraries. You can either use CDNs(Content Distribution Networks) or have JQuery libraries in your site.
Time to get dirty.
In the master page's head section, add the links to the libraries
Once you get the libraries, in the content page, drag & drop a asp:TextBox and add the jquery code to attach the datepicker to the textbox.
It should look like below.
If you are not using master page, you can replace $('[id$=TextBox1]') with $("#TextBox1"). Thats it! Just 4 files to link and 2 lines of code will get you a beautiful Datepicker on your page.