Good job Mici! The one you found is very close! I compared the pictures on the site you linked to another shot of "my" bee (below) and was able to see some differences though. If you count the stripes on the abdomen, yours has just 4, mine 5. Also the stripes seem to be of different colors, yours being clearly black and white, mine brown and yellow and shading into each other.
Still, they are more similar than different and I had so very many sunflowers in my garden last year it makes sense that some of these bees that specialize in this kind of flower would be around the area. I will plant more now that I know these beauties will visit just for them.
Shot with COOLPIX L3.