If you want a good long-lasting finish the collinite mentioned above is great stuff - used to get around 6 months decent beading and a nice shine on my old A4 cab which was driven daily and parked outside at all times.
I like the finish from Zymol Glasur on dark cars, but it does not last as long.
Never found a spray wax that is of much use, although I do use one as a quick detailer occasionally.