Interesting thread this for me as a Photogapher. Some good advice already posted here so no need to repeat anything, just remember a few things:
HDR, or ANY effect applied post-production will not make up for a poor photo... either technically, or compositionally. It's meant to enhance only.
Second: Tonemapping. Don't go over the top. The point of HDR is not to create wacky special effects, and when you do, it just looks like you've run it through a Photoshop filter, and looks cheesy. The point of HDR is to keep detail in shadows as well as highlights... simple as that. While a slight overcook in tone mapping can look good, remember.... less is more.
Don't get too caught up in the whole HDR thing.. HDR is something that you can do to photo that's already great, but it won't rescue a poor one. Take the time to look around the viewfinder first... watch for the pitfalls such as power lines, trees out of people's heads, or in this case, car roofs etc. Think about where you place the car in the frame: Don't just stand there and take it from your eye point, as usually, it's a crap place to be to take a photo. Think of getting low, or high, or maybe place the car in an unusual place within the frame. Don't just put things in boxes from your normal standing eye level.
A tutorial on photography is way beyond this thread... but Google is your friend
Some HDR stuff of my Mustang.
Another thing to rememebr, is that HFR workds best when using more than one exposure, rather than trying to create a HDR set from one. Use a tripod... take a range of shots starting around 2 stops under exposed, then 1 stop under, one dead on, one 1 stop over, then finally 2 stops over. Use those 5 to create a HDR image, then tone map it so it doesn't scream "HDR" at the top of it's voice
I use Photomatix. Not found anything to beat it so far.