LMC,
If a blower isn't shifting the spots, then you may need to use one of the other methods involving a swab or brush. You'll find a variety of methods described here:
http://www.cleaningdigitalcameras.com/
Persevere with the blower to begin with, you'll find you can shift some pretty stubborn bits if you get very, very close with the tip of the blower.
Duncan