hello, It is hard to find really original ideas on the web. Lucid dreams offer such an incredible array of experiences, however, I can only think of a few. If each person who visits this page suggests some interesting new ideas, we can all try them =)
I'll go first:

become multiple people at once, experience each person's senses

find a new magical fruit and see what your mind makes it taste like (hopefully not like any real fruit; apples, oranges, etc.)