Even sealants are not perminant - they should be used as a base to wax over. Nothing will protect the shine better than proper washing, drying, and waxing.
I have been using Liquid Glass. You can get it OTC at many auto stores for between 20-25
http://www.shopmpt.com/liquidg....html
The shine is great. It is a stackable product which allows you to build up multiple coats to give a deep shine with. Below is a pic of my S with about 5-6 coats of LG on it.
One other plug for it. When I was back in NC visiting my parents last year we addressed the much neglected finish on my mom's car, and my dad's. We went out to run a errand and ran into one of his golf buddies. He asked when my dad got a new car. He said we had just washed and LGed it. By the end of the weekend all of his golf pals had run out and gotten LG and every store was sold out. I should have been charging the company for advertisement.