Dark Horse have made available four comic books based on Mass Effect to members of their online portal that anyone (who is registered) can download for free. The comics are the Redemption books that tell the story of Liara T'Soni and the Evolution series that tells the story of Cerberus and The Illusive Man. And they represent a taste of what's to come from the next comic book chapter in the Mass Effect universe - Invasion - that explains the events leading up to Mass Effect 3.
Hop on over to Dark Horse's portal for your own copies.