Arduino(Uno or Mini) in a car?

Hello!

If using arduino in a car, should i protect it somehow from excess voltage or something? What about too low voltage? Ignition? Or just plug it in to + and - and stop worrying?

No you need to worry a car is a very hostile environment and is not easily calmed without experience. Look first at extra decoupling on the power lines:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

and then protection on inputs and outputs:-

http://www.thebox.myzen.co.uk/Tutorial/Protection.html

but that is only a start