A rough timeline (some of the stories overlap)...
Mass Effect: Evolution - A four part comic series set during the First Contact War. It focuses on the origins of the Illusive Man and Cerberus.
Mass Effect Revelation - A book set between the First Contact War & the events of Mass Effect 1. It focuses on Anderson, Saren, and the mission Anderson mentions in Mass Effect 1 that ultimately prevented him from becoming humanity's first Spectre. It also foreshadows the events of Mass Effect 1 and the Reaper War.
Mass Effect Homeworlds 1: The first issue of the Homeworlds comic series. It opens during the Reaper War, but most of the story is a flashback to ten years prior, just after he had joined the Alliance. The events though are set at home and focuses on his relationship with his family.
Mass Effect: He Who Laughs Best: A comic that is an origin story of sorts for Joker. It focuses on how he ended up as the Normandy's pilot. Set just before Mass Effect 1.
Mass Effect Homeworlds 2: The second issue of the Homeworlds series. It is set just before Shepard meets Tali in Mass Effect 1, and focuses on her pilgrimage and the events surrounding her finding the evidence that gets Saren stripped of his Spectre status.
Mass Effect 1
Mass Effect Galaxy - An I-phone game. Jacob is the protagonist, and the game is basically his origin story and deals with how he ended up recruited by Cerberus. It revolves around the mission he mentions in ME2 where he stopped a Batarian terrorist attack on the Citadel. Miranda plays a supporting role.
Mass Effect Incursion - A mini-comic focused on Aria T'Loak and a prequel of sorts for Mass Effect 2.
Mass Effect 2
Mass Effect Ascension - The second Mass Effect book. Mainly about Cerberus and set during the events of Mass Effect 2.
Mass Effect Redemption - A four part comic series that is set during the events of Mass Effect 2. Liara is the main character, and it focuses on the mission to recover Shepard's body. It is also a prequel of sorts to the Lair of the Shadow Broker DLC.
Mass Effect Homeworlds 3 - The third issue of the Homeworlds series and mostly set during the events of Mass Effect 2. Garrus is the main character and it is an origin story for Archangel and the rise and fall of his vigilante squad of Omega.
Paragon Lost - An anime. Set during the events of Mass Effect 2. Vega is the main character and it focuses on a mission against the Collectors that he mentions to Shepard in Mass Effect 3. Along with the Homeworlds comic it's sort of an origins story for him.
Mass Effect: Retribution - The third Mass Effect book. Mainly focuses on original characters introduced in the second book, but Anderson plays a major supporting role. It's mainly about Cerberus, though it also deals with the Reapers & foreshadows some events from Mass Effect 3.
Mass Effect: Inquisition - A mini comic focusing on Captain Bailey and a corruption investigation on the Citadel. Set between ME2 and ME3, It sort of foreshadows an event that is the focus of one of the main missions in Mass Effect 3.
Mass Effect: Deception - The final Mass Effect book and set between ME2 and ME3. Pretty much officially rendered non-canon at this point. An outside author was brought in to pen it, and Bioware mucked up the quality control. Besides being poorly written and having some unintentionally hilarious dialogue and scenes (some of which later became memes), it had a ton of lore errors that conflicted either information in the games or previous books. There was a bit of a fan backlash after it's release to the point that the publisher apologized and promised a rewrite. The rewrite never happened and Bioware now pretends it doesn't exist.
Mass Effect: Conviction: Set between ME2 and ME3. A mini comic that deals with the backstory on how Vega ended up crossing paths with Shepard in Mass Effect 3.
Mass Effect: Infiltrator - Another mobile game. The main character is with Cerberus and it foreshadows a later reveal with Cerberus that take place in ME3.
Mass Effect Homeworlds 4 - The final issue of the Homeworlds series. Set just before the events of Mass Effect 3. Liara is the main character, and it focuses on a mission to locate Prothean archives that might have information on a means to defeat the Reapers.
Mass Effect: Invasion - A four issue comic that is a prequel of sorts for the Omega DLC for Mass Effect 3. Aria T'Loak is the main character. Set during the Reaper War but just prior to the start of Mass Effect 3.
Mass Effect 3
Mass Effect: Blasto is Forever - As the name suggests, a comic about Blasto. Since it's supposed to be a fictional story within the Mass Effect universe, it doesn't really fit on the timeline.
The Foundation Series - A 13 part comic series. The first issue is set between The First Contact War and Mass Effect 1. The rest are set during the events of Mass Effect 2, but most flashback to origin stories of various of ME2 squadmates. If you're going to read all the comics, save these for after you complete Mass Effect 3 and the Citadel DLC however. Despite being set before ME3, these are best avoided until after because they'll spoil something that occurs in the Citadel DLC.