What is required to be driven? This determines what sort of buffering is required. Say you want to drive relays - then you may require some inverters (74hc04) and something like a uln2003 or uln2803 which will provide up to about 500mA of current sink on each output (be sure to read the maximum specs!). If you want to drive leds, then the 74ls244/240 or the hct versions may suffice. Generally the buffers can sink (pull to 0v) current better than they can source (from 5v) so the usual practice is to have the buffer sink the current - therefore one would use non-inverting style buffers so when the 8051 powers up, the port pins are high so your code needs to set the port pins low to turn the leds on.