Pyramids of Mars (Fourth Doctor).
An interesting look into Egyptian mythology Doctor Who style. The entire basis of Egyptian religion centers on a war between the various members of an alien race known as the Osirians. Sutekh worked very well in his scenes with the Doctor. It's too bad the writers decided to kill him off. A powerful alien with a desire to eliminate all other life would have been interesting to see again.
I know get the reference Sarah Jane made to mummies in the 10th Doctor episode School Reunion