what are some casual greetings?

I know おはよう（ございます）、こんにちは、こんばんは etc etc. Though, what is the equivalent of the English "hey" or "hi"? I have been told that おはよう　can be used throughout the day in casual speech, for "hey". Is that right? ＾＾

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but yo... isn't the same as hey. no one where i have ever lived says 'yo', especially girls. kind of 'ghetto'? and the travel phrase greeting site, i already know those phrases! sorry ^^