Electrum 2.0 supports a new make_seed command line option that generates a random seed and displays the mnemonic:
Electrum is a deterministic wallet where all bitcoin private keys are derived from a single seed. That means that you only have to backup the seed once and it’s good for life. It also means that should the seed be compromised all your bitcoins can be stolen. So let’s look at how electrum seeds are created and secured.
An up to date guide is available here