Is there another explanation, apart from the doppler effect, for the redshift observed in distant galaxies? On episode 10 of the original Cosmos TV series, Carl Sagan mentions that some scientist don't agree that the redshift observed in distant galaxies is evidence of the big bang, stating that probably the doppler effect is not responsible for this effect. What other explanations are there?
Tired light has been used as an explanation before, whereby light loses energy whilst travelling through space---a sort of drag effect. 

I don't think anyone actually supports it nowadays, though.