I think I'm going to buy a F80 (N80).
I used to have a F60 (N60), and the built-quality was good enough for me. I suppose the F80 won't be worse..
Also, the built-in flash, might be usefull in an 'emergency', when you forgot your other flash, or just couldn't take it with you because of the weight.
Also, I can easily get 1 year (or more) warranty with the F80, and I can simply buy it 'new'. With second hand material, you really never know what you will get..

Now I have to save some money and decide what kind of lens I want with it. I've some ideas, but still can't decide..
I'll make another thread for that..

Thanks everyone for the help.