For what its worth - I have tried Meg's Gold Class - great for a quick spruce up but does not last too long.
Colly 415 - I was using this for about 12 months and thought it was really good, lasted quite a long time (a good 3 or 4 months)
Now I have been converted to Autoglym HD - best stuff I have used. The water just runs off this when washing the car and it gives a deep shine.
Must admit that the credit card takes a hammering and my collection is starting to build up.
Also be aware, the other half likes my shiny car, so I have to do her's as well. Now my daughter has brought her first car and wants that cleaned regulary - I will have to start charging at this rate , my weekends are taken up keeping 3 cars clean. It is satisfying though.