I vote number 8. Def number 8.
You could even incorporate the idea of the colours in 2 for some uses. I'm all for slight variation in logos for certain occasions, or even just a bit of flexibility. I change the colour of our parent company logo regularly to fit with the branding of each of its subsidiaries.
I suppose you could use Google as a good example of logo variation (
http://www.imediaconnection.com/content/7732.asp). There is a danger of confusing your audience, but when your brand is as powerful as Google you can play knowing that people will still easily recognise you.
Sorry, I’m getting carried away… back to my point. I like number 8!
Cheers
Jude