Ok, this recommendation probably falls under the category of "you've gotta be kidding me." Well, here goes. . .
I bought a Foamaster Foam Gun from Autogeek, and I love it.
http://www.autogeek.net/auqufofogun.html
A fellow ET member showed it to me a few months ago and I thought, "No way in hell am I buying one of those things just to spray down the car --and certainly not for $60."
Well, after doing some research (and $60 later) I find it perfect for washing my car especially when it's absolutely filthy, usually after a track event where the car has been sitting out for several days exposed to the elements. After spraying the car, the foam sits on the surface and kinda pre-dissolves some of the dirt making it easier to remove.
It's a little difficult to explain, but the car feels a lot smoother when I take the sponge/wash mitt to it after that, and I don't feel like I'm grinding dirt into the paint. Give it a try.
No affiliation here, but thought I would share.