Wrex - Dies on Virmire screaming and ranting about how a resurgence of the krogan horde is a risk the galaxy should be willing to take in order to save his people, pulling a gun on Shepard as a result. Wrex is gunned down without hesitation.
Ashley - Activates the nuke on Virmire and dies, insisting Shepard save Kaidan and the salarians. Fights off the geth and does not hesitate, dying in the blast.
Miranda - Rescued Oriana in Sanctuary, killing her father while doing so. Miranda becomes Humanity's ambassador on the Citadel, using her boardroom and diplomatic skills to effective prioritize what issues are important. The revelations by Shepard of the racial secrets of the asari (i.e. the temple of Thessia), the salarians (uplifting the yahg), and the turians (Cerberus bomb) is something she uses to her massive advantage, gaining many bits of tech and knowledge for the humans to prosper. She shares a few of these revelations with the others, but not all of them.
Jacob - Drifts into obscurity. Brynn becomes well known for cracking some of the secrets behind mass effect technology, and makes headway on the concept of making new mass relays.
Mordin - Convinced that Urdnot Wreav will just make more war than ever, doesn't cure the genophage. In the remaining ten years of his life, he does many things, ranging from creating a cure for cancer that adapts to the host, to a rumored exceedingly deadly batarian-tailored virus. When asked about it, his mind goes a mile a minute, even by salarian standards.
Grunt - Completely unconcerned with anything around him, he fights good fights for most of his young life, eventually becoming his own warchief when Clan Urdnot is destroyed.
Jack - Continues on as a teacher, the years are their own slow form of therapy. Still never gets completely over it, but most who meet her think it's good enough.
Samara - Returns to asari space as a Justicar, ferreting out injustice wherever she finds it. However, she visits Falere once a year, on the anniversary of the end of the Reaper War. The Code does not forbid it, a loophole she learns to treasure.
Thane - Died against Kai Leng protecting Councilor Valern.
Zaeed - Retires to Bekenstein, which rebuilds itself after the war. Eventually goes crazy in retirement and finds Vido again. This time, there is no escape ship.
Kasumi - Keeps her sunny spirit even after losing Keiji and Jacob, and uses the proceeds from all of her thefts to be a very rich woman. Several good-looking men report feeling like they are being watched.
Garrus - Returns to Palaven and is honored. He's offered promotion on the various ranks, but Garrus doesn't take all of them, still feeling unworthy about Sidonis. Eventually, becomes a high-ranking advisor to the Primarch.
Tali - Returns to Rannoch. She lets the geth upload into her suit and enjoys a new life.
Kaidan - Remains a Spectre, undertaking a number of dangerous missions. The many criminals and dangers he meets darkens his personality, and he shows no mercy to the guilty. Councilor Lawson uses him to great effect.
Javik - Retires to the hanar homeworld. More water than he's used to, but with all the perks he gets, who cares?
James - Starts the N-program. Gets really drunk one night and ends up losing everything at cards, even the clothes off his back. Someone with a camera takes a few pictures and...well, James hasn't worked out the rest of the story yet.
EDI - Devotes her processing power as an AI to devise efficient solutions for rebuilding. Once that's done, EDI, who identifies as human, works as a researcher to create many new technologies, considering it the most efficient use of her power.
Joker - Succumbs to an injury for Vrolik's Syndrome not long after the war.
Kirrahe - Remains with STG, taking missions on Tuchanka killing many hardline militant warchiefs. Convinces his superiors the dangers of the yahg outweigh the benefits.
Wreav - Dies on Earth, along with many krogan, because of their rampaging tactics.
Victus - Uses his ruthless nature to lead the turians in a different fashion than the normal way. When separatists arise, as they tended to, they were dealt with viciously.
Linron - Keeps her word, but is assassinated shortly thereafter. No one knows who did it, but that's true of many good salarian assassinations.
Aetheyta - Silently enjoys the fact that most of the Matriarchs who "laughed the blue off her ass" died on Thessia with their heads in the sound. As one of the few Matriarchs left, Aetheyta teaches others the merits of an alternative path, and the asari begin to develop their own technology, rather than take Prothean castoffs
Eve - Convinced Shepard of the merits of the krogan, before she died. Shepard wondered if there were other krogan like her, and saw more who would rather be like Warlord Shiagur. The krogan react with war after they find out about the genophage, but with no warships, they only fight each other. Few krogan are left at the end.