May be worth doing half the bonnet and half the roof instead as it'll make it easier to compare side by side.
I haven't purchased a sealant yet (want to use up existing products rather than having heaps of half used bottles sitting around) but I did some research and a few of the products on this page are pretty good and were highly recommended on the detailing forums.
two step products (clean surface and than apply)
http://www.waxit.com.au/products.asp?cat=7
Einszett Glanz Wax. (you have to prepare the surface first)
Duragloss #111 CCP. (ditto)
These are one step products
Duragloss #101 Polish & Cleaner.
Duragloss #105 Total Performance Polish.
No matter what product you use even if it's just a wax I'd recommend a product like Duragloss #951 Aqua Wax. You spray it on after rinsing the car and use a microfobre waffle weave towel to dry the car and it gives extra protection. Adds less than 5 minutes to the wash process.
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