If you have a Roku streaming device, you now can also get the CW Network for free. The CW is where Supergirl moved to after the first season on CBS. This a pretty nice free addition, as the CW has quite a bit of programming, including Arrow (and other non-superhero content, too).
The CW Network is also available to subscribers of Hulu, on their commercial-free tier.
BetaNewsRoku promises "The CW channel will give all Roku customers access to the current season of shows including The Flash, Supergirl and Arrow. New episodes are available the day after they air, with the last five episodes available at a time".