Recommendations for traveling in Asia?

Hi, I am in the middle of planning for a trip to Asia this fall. A friend of mine who spent a year teaching English in China and who studied Chinese for her degree is heading back as a tourist. I actually don't know yet if we will be spending much time in China. Plans are still tentative but may include: India, Japan, South Korea, China, and any place where a familiarity with Mandarin might be useful.

Does anyone have any suggestions of places to visit or things to do? General advice on traveling in the region is also helpful!