Griot's is the only stuff I'll allow to touch my M3. $40/gal

The Most Important Step In Proper Exterior Car Care Is A Safe And Thorough Cleaning
This is the MOST important step for paint preservation, yet many people overlook this crucial element when caring for their finish. Many of the mild scratches you see in your finish are from aggressive washing. The dirt acts like sandpaper, scratching the finish while you're rubbing the surface of your vehicle. Be gentle while washing, and frequently rinse out your mitt or brush during the cleaning process. With Griot's Car Wash, the first thing you'll notice is how slippery it acts between your wash mitt and the paint. This is an important characteristic of our Car Wash and contributes to its ability to lift away contaminants while protecting the finish during your washing therapy. Griots Car Wash is gentle on your wax, yet removes more dirt and road grime than any car wash I've tested. Safe for all paints. We've included a unique measuring scale right on the 16 ounce bottle's label and an easy pour spout to reduce waste. Save some money, buy it by the gallon, and refill your bottle. Our Car Wash is environmentally friendly too.