1) King Cailan (Simon Bird)
One of your first major missions (outside of the ones dictated by your chosen species and background) involves heading to Ostergar to become a Grey Warden, one of the brave soldiers tasked with defeating the Dark Spawn threat. It's here you're introduced to King Cailan, leader of Ferelden, the people's great hope for salvation. Only he sounds like Simon Bird. You know, Briefcase out of the Inbetweeners. It's very difficult to accept him as a noble but reckless leader hankering for the glory of battle when you keep expecting him to beg Jay to stop saying clunge.
2) Niall (David Bowie, sort of)
I really hate any kind of dream sequence in anything. I know that artistically-speaking the Scarecrow sequence in Batman was a stunning piece of design, but it just pissed me off. If I wanted to play Scarecrow's Weird Power Fantasies then I would, but I don't want to play that, I want to play Arkham Asylum and enjoy punching thugs as Batman. Same goes for DA:O and the mother-fucking Fade. I have no interest in walking around really slowly as a ghost mouse. While I'm sure Ghost Mouse could be totally awesome, I don't want to be forced into playing it when I'm in the middle of fighting abominations in the Circle Tower. But what the Fade has in it's favour is Niall, an unfortunate Blood Mage who has the voice of not only David Bowie, but Jemaine Clement being Bowie in Flight of the Conchords. You have to hear it to truly appreciate its wonder.
3) Bodahn Feddic (Eric Idle)
Bodahn is a particularly weird one, because he's actually voiced by Murdoch from A-Team, Dwight Schultz, which would probably be more disconcerting than who he actually sounds like, which is Eric Idle. Boring as Bodahn is, I like listening to him talk because it takes me back to the Discworld video games (Idle voiced Rincewind) and a time when story-based point and click adventures were games, no arguments and you didn't get hordes of miserable internet commenters denying their validity as part of the medium because they don't contain gunbros.
4) Zevran (Mandy Patinkin/Antonio Banderas)
I saved Zevran till last because, due to the countless hours of recording his poor voice actor had to endure, his voice fluctuates between two (admittedly fairly similar) famous voices. When you first encounter Zevran and he's intent on doing you in, he has an air of Íñigo Montoya about him. Later, once he's joined your cause and softened to the idea of being your manslave (He's my manslave. if he's not yours, you're just failing to capitalise on what's there.) his voice takes on a more sultry, Banderas edge. Either way, whenever I play as Zevran, I imagine him saying "My name is Zevran Arainai, you killed my girlfriend, prepare to die." as he kills his foes.