Don't bother praying for the health of others. Surprise! It doesn't do diddly-squat for them, even if they know about it.
"Praying for other people to recover from an illness is ineffective, according to the largest, best-designed study to examine the power of prayer to heal strangers at a distance."
Naturally, it's entirely possible that saying the prayers may make YOU feel better, however.
Update: I always find it interesting when people dismiss research findings out-of-hand that they happen to dislike, without reviewing the actual study. An abstract of the study is here, and an editorial discussion of the findings is here. (May require registration).