This is a wheel that\'s been re-invented again and again over the years.
The Problem: The user needs to input a Date/Time
Basic considerations
A text box with an image-link to a pop-out calendar on the side is my choice. Best of both worlds.
If you want something extra you could let a natural language date/time parser like Chronic http://chronic.rubyforge.org/ spice it up.
Also don't forget the international users.