I have for years used a javascript for selecting dates - looking like this:

and when pop up:

As I said it has served me well, until recently. I needed to be able to select time as well. First step is to look around. And I found this one:
JSCalendar

It looks pretty don't you think! However - it was a pretty nasty Javascript interface to configure it - don't take me wrong - it's probably not nasty for someone eating Javascript every day, but for me - I felt I needed a control to hide some of the hard to rememberJavascript stuff.
While the JSCalendar can ne configured to do pretty much anything, in just about any way possible, my requirements were much more modest - so, first of all, lets start there by looking at my requirements:
- a (readonly) textbox and an image for triggering the popup. Cause popup is all I need. No editing in the textbox or anything - changing dates are done through the popup, period.
- support different types of format.
- support time editing - but also be able to function without it
- possible to use with standard ASP.NET validation routines