I just replaced my thermostat and I went for a test drive around the block to try to heat it up. The first time around the block was fine, but a few minutes later, at the next stop light the oil light started blinking and it sounded like it had a nasty ping. I got on it and out of the rear view mirror i noticed white smoke coming from the exahaust. Now the car is making a bad ping at idle and I can hear a knocking from the top part of the motor. Any ideas? Please help!!!

white smoke or blue?

Blue is generally oil and white is most likely water/antifreeze (head gasket??)

Check the oil if it is a milky bubbly mess then anitfreeze is mixing with the oil somewhere.

You have air in the system... do not drive it any longer until you fill the coolant system properly through the coolant crossover tube or you may damage your engine for good!

It sounds like you didn't bleed the air out and your head gasket may have blown.

I agree, white smoke is usually a headgasket.

usuallly head gasket is true but I have seen some cars with intake manifold gasket was as fault. Fill it up correctly and maybe you will get lucky.
when you fill it let it and constantly check it. Also wait till the cooling fan to turn on before you test drive it. if it does at lease most of the air will be out. when you test drive check everything again when you get back. it might a little messy but check everything ! ! ! ! inclueding oil level and trans level. Make sure the color still looks good. I have seen them over heat bad enough to cook the fluid in there too !!

If it's "pinging" as you say at idle then I will strongly assume that you mean it's knocking which means the engine is toast.