How about used coffee grounds as mulch?

Without a soil test, I would not assume that high pH is your azaleas' problem. Are the plants recieving adequate moisture? Are they competing with the roots of hardwoods? Are they getting too much sun? Is the pH already too low? Have azalea lace bugs attacked the plants?

Used coffee grounds are almost neutral in pH and not helpful in acidifying soil.

The above advice is very sound. Without knowing what your soil's pH is to start with, it is not a good idea to search around for amendments to alter the pH.

Keep your azaleas well mulched at all times, and you may want to consider one of the fertilizers for iron loving plants once you've ruled out other reasons for off color plants. I much much prefer the organic, slow release benefits of Holly-tone, rather than the soluble Mir-acid.

if you've checked the soil... i put some lemons (after squeezing for cooking :) and wrinkly tomatoes around the base of my pieris japonica to make the soil more acid.

be warned, though -- i didn't expect to see a tomato plant explode through the leaves of the pieris!

NC does soil tests for free. This is a fantastic deal. What county are you in?