I've had a few stuck bits of crud that wouldn't go with a blower or the dust removal feature. What did work was getting them to move a bit with the brush end of a Lens Pen then finishing off with a very strong blow aimed at the right spot on the sensor, it's no good just blowing it generally all over the sensor from an inch away, you have to get closer (carefully). Bear in mind that a spot that is visible on the upper left corner of your test shot will be caused by dust in the lower right corner of the sensor as you face it.
Last edited by SteveB; 10-14-2013 at 01:20 PM.