There is a ton of fun stuff to do on Maui, it really depends on what you are into.
I am not going give you my opinion here because I have not done many of the
activities offered. Listed below are some good links that will give you
a good overview of the types of things offered.
However, these sights are in no way complete, they push some things more
than others. Some don't even list vacation rentals in Haliimaile (us), some nerve yah!
Anyway, take your time, you can get great deals when you arrive, (except Christmas
time), so don't feel pressured.
My only advice to you is this. Don't try and do too much while your'e here. Relax and
enjoy the beauty of the island. Watch a sunset on the beach. It's free, it happens
everyday, and it is one of the most beautiful things you will see on Maui. I guess I ended
giving you my opinion anyway!