7-8 hours is recommended..everyone is different of course.
there was a time that i couldnt get a straight 8 hours sleep..i'd wake up 3 hours into my sleep...falll asleep then wake up again 2 hours later...etc.
some tips i've read from men's health magazine to get a good night's sleep are:
*go to bed at the same time, and wake up at the same time as much as possible...even on the weekends.
*no caffeine, sodas, coffee, ect before bedtime.
*don't nap...naps keep you from getting the long REM sleep at night.
*your bedroom should be a place where you sleep and have sex ONLY..this means no tv, no computer, no reading...these things all cause stimulation of your mind.
*a soft jasmine sent kept around the bedroom and used only in the bedroom can help you associate the smell of the jasmine to sleep and may help you fall asleep faster.