I used the SB-600 for all of these shots except for the 1st one of the blue Subaru, I had the Sto-Fen Omnibounce on for all of the pictures taken with the flash. I was talking to Mark-A (above) earlier and he reckoned that I should've taken it off for the model shots and used it without, I think he was right as the background is a bit dark on some of them so I'll try that next time and just use the Sto-Fen for the very reflective cars.
I'll look into that cable, but it was very tight with a crowd of people around you all the time. I expect all the shows will be like that. Although, it's amazing how many people move out the way to let you past when they see you have a DSLR which is bigger than a compact!
Seeing as you've progressed to the D200, you can run without the cable and use the wireless command facility with the SB-600.
As for the omni-bounce, remove it when you find that your flashgun doesn't give you enough power. Otherwise keep it on, especially when you're taking portraiture - an undiffused flash causes a horrible colour on skin.
On the matter of portraiture, it's better to forget the background detail - the less clutter you have, the better, and here I side with Alex. The darker background isn't a negative.
As Bob has hinted/suggested, you (and also Mark-A) should start playing with apertures and depth of field. There is too much front-to-back sharpness, and when you're taking subjects like people and cars, it may be beneficial to single out the subject from the environment.
To me, I'm not convinced you've learnt to control your apertures from your sample images. Let me briefly give some feedback on your initial images:
Image 2: there is some visible diffraction here as you've gone to a very small aperture. The image isn't sharp partially down to this, but also handshake. At f22, you need a long shutter speed to get the light in, and at 95mm, you should be using 1/100 (purely by reciprocals). A wider aperture, say f8, would give you a better result if you wanted sharpness front-to-back. In this case, I'm wondering if you're trying to focus only on the NO canister - if so, then use the widest aperture available to you, as well as controlling the distance to your subject to achieve some bokeh to single it out.
Image 3: There's no focal point to this image, which could again benefit with some DoF control. If you're going for front-to-back sharpness, f5 won't give that to you. You can see that the sharpness drops off slightly to the sides of the car.
Image 4: The framing isn't right here in many ways. You could have gone close for an upper body + shoulders + head shot, or stepped back and zoomed out to get a full length shot. Cutting the legs off the frame is a big negative. The model is also quite central in the frame. Here I'd be wanting to move the model to the left third of the frame and have more room leading on the right. Once again, DoF could be reduced with a smaller aperture to isolate the model from the environment.
Image 5: Be careful with shadows - you might have captured your own shadow and possibly your arm (bottom left of frame). Other than that, the image is partially over-exposed - most evident on the white in the background.
These were my immediate thoughts when I viewed your images. I don't mean to be deliberately harsh. When are where are your next events? Are they based around the south of England? Can you PM me details?
Finally, thank you for sharing your work.