I will start with the absolute basics, then include a few more ideas later on. If you already make soap and are just looking for new ideas, you might want to skim over the basics and head to the end!
Just a note: Melt and pour soap could be considered a 'cheat's' way of making soap, as you purchase pre-made soap base, melt it and add things to it. I like it because it is ideal for a small kitchen, very forgiving and easy to be creative with. It would be an ideal project for kids, though under supervision only - the molten soap can get very hot, and before melting it usually needs to be cut up with a knife, so please be careful!
An inventive example of what you could do with M&P soap can be found here.