For car audio Image Dynamics is a very good product and normally at a much better price point than their main competition (IMO that would be JL Audio).
A very good small box car audio woofer is the RL-i eight (web page reference:
http://www.soundsplinter.com/rli_series/rl...formation.html)
This woofer is made for Sound Splinter by TC Sounds and is essentially the TC2+.
If you thinking of getting a woofer and need an amp too, these guys give package deals:
http://www.edesignaudio.com/product.php?ci...d=1&cur=USD
At a more reasonable price I'd look at this unit for a single 8":
http://www.partsexpress.com/pdf/295-545s.pdf
My personal recommendation would be to look at woofers made for home use & here's why I make that recommendation. Car audio woofers are mostly designed to be used in a coupe/sedan. Since you are essentially "inside" the enclosure when the windows are closed there is an effect called cabin gain. What that means is that starting around 100Hz, and moving down in frequency, there is a 12dB per octave gain due to being inside the car (Just to be clear, the cabin gain is size dependent (less gain in an SUV than a Honda CRX for example). Convertibles have almost no cabin gain even with the top up & windows closed, the roof just isn't rigid enough to count (now if you buy the Toyota hardtop...).
In the home area there are many choices, you might take a look here to see comparisons/recommendations:
http://ldsg.snippets.org/index.php3
FYI, I use two of these (but would have picked something different if I was just going to have one)
http://www.partsexpress.com/pe/showdetl.cf...tnumber=295-366
and finally, if price is no object look at Focal, Eton, Seas, Skanning....