Quote Originally Posted by SmartWombat
You need to shut the lens right down to see the spots.
In case you're not sure what this means, set the lens at the lowest aperture (highest "f" number, like f22). Shoot a piece of white paper or a clear, wide open blue sky. Wider lenses usually help here too, due to the depth of field. Compare the shot to just looking through the camera and hitting the depth of field preview button on the camera.

With a blower, you could have just simply moved a piece of dust from one spot inside the mirror box to another; like the mirror to the focusing screen. Eventually it'll find its way to the sensor. That's the problem with blowers versus a vacuum. Try holding the camera upside down (open mirror box pointing towards the floor). This way dust can fall out aided by gravity, rather than fighting it.

Dust can get inside cameras almost regardless of how careful you are with your gear. Be careful to do your best to keep it out of the camera, but at some point you'll need to remove it.