Recently I came across a good date picker called Kalendae that doesn't need any additional framework code, it just works.
Nice UI and clean code. Might choose this over an ASP.NET Calendar, just for load time alone. Although, I wonder why they went Open-Souce, with so much dedicated to the project, I would never release it for free.
I love how they went pure JS.
JS > jQuery
Old Skool style.