I have just watched Aelita and thoroughly enjoyed it. Can anyone recommend any other silent era science fiction films that are worth a watch? Besides Metropolis that is, I've seen that before too.
You might also want to see the early talkie "Just Imagine" (1930), which is the first (to my knowledge) sci-fi/comedy/musical. Hard to find, but lots of fun, and it makes a great break from so many of the films that take themselves too seriously.