"What's up?" is in spanish is "¿Qué pasa?" and "How are you doing?" is "¿Qué estás haciendo?"

que mas, como andas?, que onda? , como te va? well this what i most remember now

Ademas uso "que tal?" y "Como estas?"

What´s up? = (formal way) Que pasa?!! = (informal way) Que pasa tio!!!? How are you doing?= (formal way)Que estás haciendo?= (informal way) Que haces tio!!? more or less :p I Hope that I helped you :)