I used ardamis fix, with one difference: instead of completely eliminating the $sep variable, I just eliminated the spaces to either side.
So, I changed:
$prefix = '';
if ( isset($title) )
$prefix = " $sep ";
to
$prefix = '';
if ( isset($title) )
$prefix = "$sep";
My title tag now looks like this:
<title><?php if ( is_single() ) { wp_title($sep = ''); ?> :: <?php } ?><?php bloginfo('name'); ?></title>
This gets rid of the extra space and adds a "::" after the title of your post, while maintaining no spaces between "<title>" and your blog name if it is your main page.