[T-Mobile myTouch 4G Slide] Blue6IX:
I've been using the generic T-Mobile Universal Car Cradle, and it works pretty well. I've only tried it in portrait, but that's how i'd rather have it anyway.

You can see how I have it mounted in the pictures below, what you can't see is that I didn't use the sticky stuff to hold the plate for the suction cup on. I took out a screw that holds my dash in, and found another one that came out far enough to use to hold the plate in place. I drilled a hole through the center of it, and after putting a metal washer at the end of the screw makes an air-tight base for the suction cup.

It's not falling off...ever. The sticky stuff is just a bonus at this point, because it isn't strong enough to hold the contraption to the dash upside down like that on it's own.

I'm using the generic T-Mobile universal micro-usb car charger to power the cradle.

The cradle is adjustable, so the side pieces can be let out far enough to fit it snug without squeezing it. The bottom piece that it rests on is adjustable downwards, as well, so you can get the micro-usb slot exposed on the phone.

I ran the cord from a power port on the passenger side of the dash, and zip-tied a spring clip in under the dash to hold the cord out of the way. Coiled cord shines in this regard, the coils keep it from sliding around.

The coils also let it latch on to the post holding the cradle to the dash, so it doesn't get in the way of my legs when i'm driving.

The whole setup is rock solid, and all I have to do is listen to the GPS. If I have to change something on the device, my hand is already near it, so I don't have to reach across the vehicle or up on the dash to get to it.

Also, it's not shining in my face while i'm trying to see out of the windshield at night. It always bothered me to have the bright light from a GPS, even in night mode, just right on my dash. I can see much better with this mounted low, then I could with my standalone GPS suctioned to the windshield.

It doesn't interfere with my shifter, and my key ring for the vehicle is small, so nothing dangles low enough to hit or scratch the device.

After I started driving around with it and using maps, I had to get a cradle of some kind. None of the T-Mobile stores near me had an official myTouch Slide cradle, and I needed one right away. I figured i'd get the generic one once the sales rep and I realized it would work, and just upgrade when I got the chance.

I don't think I want to get the official cradle, I like the setup I have now.

This won't work for everyone, and you can't use the real camera on the back of it when it's in the cradle, so on that token the official cradle is better.

I did notice that people seem to have trouble with, or be unable to use the official cradle in portrait mode, which I prefer for GPS stuff. Hope this helps someone!

Edit to add:

The first picture is taken from the perspective of exactly what I see when i'm sitting in the seat, that's why the third picture gives a better look at the setup. I thought it might help to see it the way I see it when i'm using it.

I can still reach all my guages and switches in the center of the dash without the device getting in the way, and the bonus is that the generic car charger also gives a free usb charge port right by where it plugs in to the dash. This means a passenger has a usb charge port on their side of the vehicle and can charge without getting in the drivers way.

I'll cut the extra length of zip-tie off sooner or later, i've decided that I like the setup and wasn't going to bother before making that determination. I'm glad I thought to take the pictures before I did as it makes it easier to see how it's put together.