How does one say 'do you want anything else' in Spanish?

If asking one person informally - '¿Quieres algo más?'
If asking one person formally (client, someone you don't know) - '¿Quiere (usted) algo más?'
If asking more than one person informally (though this is not used in Latin American Spanish) - '¿Queréis algo más?'
If asking more than one person formally or those who speak LatAm Spanish - '¿Quieren (ustedes) algo más?'

Just be careful:

MÁS --- more; else: ¿Qué más se le ofrece? --- Do you want anything else?

MAS--- but, nonetheless: ¿Quiere usted algo? Mas no se decide --- Do you want anything? But you do not take the decision.