I am a big fan of easy basing, so a while ago I started experimenting with creating washes out of heavily diluted GW foundation paints. Eventually I settled on a dusty desert world look. Originally this style of basing was created for my Blood Angels, but after painting up my first Necrons, and reading that they had a penchant for destroying imperial worlds, I decided to use the same style for their bases.
Step 1: Glue a bunch of imperial debris on the top of the flying bases. Cut the debris up as much as possible so there there are plenty of grooves for the wash to settle into.
The end result is a simple base, with enough color variation to really help models stand out.