If you are concerned about the relay turning on momentarily at power up, you can modify the FET driver to add a delay element like so:



V1 is the output of the 8051 port pin, R3 is a pull-down to ground, while the combination of R4 and C3 adds a delay element to the FET turn-on time. M3 can be any enhancement mode NFET so long as the thershold voltage is around 2-4V, and most FETS have diode D4 built in. L1 is the relay coil and R2 is a model of the relay coil's resistance and is only used for SPICE simulation purposes (don't include it).

A simulation with power being applied at t=1ms is:


As you can see, you have roughly 3 ms from the time power is applied to the time the relay turns on in which to set the output port pin low and prevent the relay from activating. Even on a traditional 12 cycle 8051 clocked at 1 MHz you still have 250 free instruction cycles in which to pull the port pin low before the relay activates.

You may still want to add a buffer between the 8051 port pin and the rest of the circuit to prevent any kind of back EMF caused by the relay turning on and off from affecting the 8051. And come to think of it, most buffers have /OE pins which tri-state the outputs if pulled high. So if you don't mind using two port pins, tie one to the /OE line and one to the buffer input. Upon reset, the buffer outputs will be high-Z until you instruct the uController to pull the port pin connected to the /OE line low.