I recently decided to dedicate my old iPod nano as my "car-tunes" device and since the battery is getting weak I wanted to ensure consistent power for long trips. I bought 2 USB adapters for the cigarette lighter from overstock.com. They are about $3.50 each and decided to convert a blank switchplate on my Honda's dash into a USB power port.
There is nothing revolutionary here, just wanted to add my variation on the theme. I wanted it to look as OEM as possible. I think it turned out real clean.

Tools:
Dremel with shaping bits
Soldering wand
solder
flux
x-acto knife
screwdrivers
USB 12v power adaptor
hot glue gun
glue sticks

about 1.5 hours total time

Step 1: The USB Power Adapter

It didn't take long to find inexpensive 12v USB power adapters. I found these at overstock.com and they are from eforcity (not a promotion). I was looking for something with a small form-factor and that appeared easy to disassemble. I bought two ($3.50 ea) in case I messed one up, but didn't. I put the second one in the "power port" in my wife's car for the kids to use.

Step 2: The Console Face

It is pretty easy to remove the console face completely from the car. I suggest that you do so that you can work on the bench and not in the car.

Step 3: Preparing the Blank

I will skip over the dremel and knife work, you know what to do. I started my holes using the drill press for control, especially for the LED opening. I needed to remove some material from the back of the blank to get a nice fit. I finished the edges of the opening with a jeweler's file to get a nice edge.

Step 4: The USB Device

Once the adapter is open, it is easy to see how simple the installation will be. I de-soldered the "hot" spring and one of the "neutral" contacts. I was going to re-solder both using the PCB spots but couldn't get the "neutral" wire in, so ended up soldering it to the other "neutral" contact. No-biggie.
The last picture is the dry fit before I glue it in.

Step 5: Installed in the Blank

I shrink-wrapped the power wires individually and then again together to hold them firmly. The leads are about 12 inches in length, which turned out to be a good idea. I needed extra wire to get around the radio when the whole thing is installed.
Then, I called on our good friend, Hot-Glue, and sealed everything in tight. Since this was deep, I made several small applications around the PCB to make sure everything was secure.

Step 6: Finished Fit

Everything is in place and it looks great. Going for that OEM look!

Step 7: Power Connections

My plan is to draw power from the 12v feeding the lighter socket. The ground is obvious and so is the power. I used scissors to remove the black wire sheath to expose the wires completely.
In the fourth picture you can see how I plan to attach my power wires in-line with the existing wiring.
In the last picture you can see that I have soldered the wires together and have the shrink wrap already for assembly.

Step 8: Reassembled!

I tucked my USB cable under the console fairing and ran it through to the glove box for storage when not in use.
The red LED lights up when powered up and looks very clean. The picture is a little blurry because it was dark by the time I finished. I will post a day-light pic so you can see it better.
I hope this has given you ideas for where you can easily place a USB power port in your car!