Question

What usually causes a large gap in excessive whitesapce on webpage like this one:

http://beta.globerunnerseo.com/contact/

Answer 1

#sidebar-sm #blog span, #sidebar-sm #facebook span, #sidebar-sm #twitter span, #sidebar-sm #linkedin span, #sidebar-sm #quote span {
left:-999em;
position:absolute;
top:999em;
}

It’s the top:999em. I think you were supposed to specify negative for the top, not positive ( eg top:-9999px or top:-999em )

Even if validating doesn’t resolve the issue you should strive to make your page valid before asking to save time.