"What are all of these spots on my print? I've cleaned my lens; so they're not from there!"

These are probably spots from dust on your sensor. This is the bane of digital photographers who change lenses. Even the newer cameras like the Canon 40D are susceptible to this despite their built-in "sensor cleaning" routines that vibrate the sensor. The newer cameras also often have special coatings on the sensor that are supposed to prevent the dust from sticking to the sensor. I've found that I still get dust sticking to the sensor despite all of these things.

I keep my sensor clean with a 3-step attack. I put the camera into sensor cleaning mode and try these in order until I've cleaned the sensor. After each step, I shoot something with an even tonality like the blue sky or a gray card or an ExpoDisc or similar or look at the sensor with a lighted magnifier designed for that purpose.

1. Move the dust by blowing it with a Giottos Rocket Air Blower. I have the large size because when I got it, that was the only size available. Now, I'd probably get a smaller one. Also, I might just get everything I need, including the blower directly from VisibleDust.com. (See next items)
   Small: http://www.bhphotovideo.com/c/product/388983-REG/Giottos_AA1920_Rocket_Air_Blower_.html
   Medium: http://www.bhphotovideo.com/c/product/318545-REG/Giottos_AA1910_Rocket_Air_Blower_.html
   Large: http://www.bhphotovideo.com/c/product/259157-REG/Giottos_AA1900_Rocket_Air_Blower_.html

2. If I still have dust spots, I use an "Arctic Butterfly" from Visible Dust. This is not something I'd do while in a place like Antelope Canyon. I'd do it at home or while in the car with windows closed. I bought mine directly from VisibleDust.com. However, B&H are now carrying it, too.
   http://www.visibledust.com/

3. When the previous two tries fail, the only alternative is to use something that's designed to clean the sensor by touching it. There are several products that claim to be able to do this without damaging the sensor. However, I've chosen to go with VisibleDust because they were the first to offer such products and because they continue to have a good reputation. Their swabs are different sizes. You should choose the ones that are for the sensor size in your camera. I have

Also, a lighted magnifier is a good thing to have in your toolkit. Again, I recommend the one from VisibleDust. If you order directly from VisibleDust, remember that because they're a Canadian company, their prices are in Canadian dollars.

Here's my "bottom line" on the sensor dust problem. Get everything you need directly from VisibleDust.com.