Some athletes/teams who noone mentioned until now:
Athletics:
All russian medallists in athletics might miss the olympic games.
Björn Otto (silver in mens pole vault) is very unlikely to qualify. The same might be true for Hadadi (silver in mens discus throw).
I think Savinova/Poistogova (gold and bronze in womens 800 m), Alptekin/Bulut (gold and silver in womens 1500) are banned?
Basketball:
Russia (bronze in 2012) wont qualify in mens basketball.
Boxing:
Campbell (gold in 2012) turned pro, i dont know if he will try to qualify. The same is true for Nevin (silver in 2012), Ogogo (bronze in 2012), Joshua (gold in 2012).
Maybe there are other athletes who turned pro and wont try to qualify.
Slalom canoeing:
In slalom canoeing it could become very interesting, because only one athlete from each nation can qualify, so guys like Tasiadis (silver in 2012) or Aigner (bronze in 2012) might easily miss the olympics.
Track cycling:
Förstemann and Levy (both won bronze in mens team sprint in 2012 and Levy won silver in mens keirin) might very well not qualify.
Ed Clancy (bronze in mens omnium in 2012) also might miss qualification, Cavendish seems to be more likely to compete in mens omnium for GB. Clancy might compete in mens team pursuit instead.
Equestrian:
Langehanenberg won a silver medal in dressage team in 2012, but she wont qualify for Rio, the same probably will be true for Schneider, who was in the same team.
Fencing:
Germany won bronze in mens team foil, but didnt qualify for Rio. Joppich at least qualified individually. Japan won silver in London in mens team foil, but only Ota qualified this time.
Vezzali won bronze individually and gold in the team in London, but this time she missed qualification. Russia and South Korea won silver and bronze in womens team foil, but this time both nations were only allowed to qualify 2 athletes, so some of their medallists from 2012 will miss Rio, the same is true for mens sabre.
Swimming:
I think it will be pretty difficult for Cielo (bronze in 2012), Jamieson (silver in 2012) and Beisel (bronze and silver in 2012) to qualify.
Shooting:
Tons of athletes who won a medal in London and are young enough to still compete (and therefore probably didnt retire) didnt won a quota place for Rio (until now).
For example:
Cox, Narang, Moldoveanu, Tesconi, Zlatic or Rossi!
Tennis:
Sharapova (silver in womens single in 2012) might miss Rio.