We have some people who whish to have (as well as a next and previous month) a next and previous year, so I have made a few adjustsments. I hope you will find them useful, and include them in the package.

date_input.css

Line 48:
.date_selector .prev {
right: 20px; // Was 5px;. changed to make room for prev year a tag
}
.date_selector .next {
left: 20px; // Was 5px;. changed to make room for next year a tag
}

Add these lines: // to position the next and prev year a tags.

.date_selector .yearprev {
left: 5px;
}
.date_selector .yearnext {
right: 5px;
}

date_input.js
line 53:

var monthNav = $('

').append(
$('«').click(this.prevYear),
" ", // add the previous year a tag to the nav
$('‹').click(this.prevMonth),
" ", this.monthNameSpan, " ",
$('›').click(this.nextMonth),
" ", // add the next year a tag to the nav
$('»').click(this.nextYear)
);

3 New functions.
line 196:

moveYearBy: function(amount) {
this.selectMonth(new Date(this.currentMonth.setYear(this.currentMonth.getFullYear() + amount)));
},

prevYear: function(){
this.moveYearBy(-1);
return false;
},

nextYear: function(){
this.moveYearBy(1);
return false;
},

add "prevYear" and "nextYear" functions so they can be used on the a tags
Line 38:

this.bindMethodsToObj("show", "hide", "hideIfClickOutside", "selectDate", "prevMonth", "nextMonth","prevYear","nextYear");

Bug(and fix) when using the date_input field in a template (including the initialize command) if you the template in multiple times, the multiple initializers would each make a calendar for each one (so 2 fields would result in 4 calendars, and you'd have to click twice for the two calendars to go away)
add intialized class to date_inputs that have been initialized (end of file) around line ~285:

$.fn.date_input = function(opts) {
this.addClass('initialized'); //Added class initialized to inputs that have been initialized
return this.each(function() { new DateInput(this, opts);});
};
$.date_input = { initialize: function(opts) {
$("input.date_input:not(.initialized)").date_input(opts); // search for date_inputs that haven't been initialized alread.
} };

})(jQuery); // End localisation of the $ function

Thank you for reviewing these changes!