Existe la abreviatura hetero, que se usa en niveles más cotidianos, pero no conozco ninguna palabra cotidiana alternativa.

I don't believe there's an equivalent in Spanish for straight. The 'hetero' abbreviation, like Lucas said, is the closest I can think of. 'Maricón' is a slur though, please don't ever use it.

You can say "él no es gay" or "él no es maricón". Both have the same meaning. Remember that in some cases there isn't exac translation.

"El no es gay" es la manera mas fácil de decirlo

There is in fact one word equivalent for straight in spanish and that word is "normal'. The truth is that in spanish it is not common to question if a man is straight , in fact the question is always if a man is gay (gay is an english word commonly used in spanish) cause if a man looks straight there is no reason to question it. And if he looks gay the first thing you question is that if he is gay .