A modification of Randy Drisgill's "Sticky footers in SharePoint" for SP2010. Works for me...

stickyfooter-2010.js

// Place the #custom-footer directly after the close of #s4-bodyContainer, and apply float:left to it.

// What needed changing: 
// - consistent use of the jQueryFooter variable (rather than re-selecting the footer to apply the margin-top)
// - changed/simplified the math to calculate the difference, adding s4-mainarea (which floats:left and is not included in bodyContainer)
// - did not force footer to show in dialog boxes (use .ms-dialog #custom-footer {display:none} in CSS to hide)

// http://blog.drisgill.com/2013/01/sticky-footers-in-sharepoint.html

// jQuery.noConflict();

function calcFooter() {
    var jQueryFooter = jQuery("#custom-footer");
    var footerheight = jQueryFooter.outerHeight();
    
    //hide footer allows for smoother window resizing
    jQueryFooter.hide();

    var bodyheight = jQuery("#s4-mainarea").outerHeight();
    var bodyareaheight = jQuery("#s4-bodyContainer").outerHeight();
    var jQueryRibbon = jQuery("#s4-ribbonrow");
    var ribbonheight = jQueryRibbon.outerHeight();
    var windowheight = jQuery(window).height();

    //if ribbon is hidden, size is zero
    if (jQueryRibbon.css("display") == "none") {
        ribbonheight = 0;
    }

    //if content is less than the window size add margin
    var difference = windowheight - bodyheight - bodyareaheight - ribbonheight - footerheight;
    if (difference > 0) {
        jQueryFooter.css("margin-top", difference);
    }

    //show footer after calculating
    if(!jQuery("html").hasClass("ms-dialog")) {
        jQueryFooter.show();
    }
}

jQuery(document).ready(function () {
    calcFooter();

    //change footer with window resize
    jQuery(window).resize(calcFooter);
});

Thanks for this post. It was extremely helpful. I am finding one issue. When I go to edit a list, the sticky footer does not "push down" or stick to the bottom when there are just a few items or no items in a list. Do you know what needs to be updated in the javascript to address this issue? Once I refresh the page after editing, the footer sticks to the bottom.
Thanks!