Check the table seen below for a complete list of nine followers (not counting the golem from the DLC). Keep reading to find about the advantages of having them as your active team members and to find out how to locate them.
ALISTAIR (human, warrior)
He joins the team automatically during the course of Joining the Grey Wardens quest [Ostagar].
Info: You should have Alistair in your team even if you're also playing as a warrior, mostly because he'll have a lot to say during the conversations and he'll also be helpful in defeating monsters.
Bonus for good relations to: constitution
LELIANA (human, rogue)
She joins your team in [Lothering - Dane's refuge] after you manage to deal with Loghain's soldiers.
Info: I would recommend having them in your team for most of the game, assuming that you're playing as a good character. Leliana can be helpful while fighting enemy troops (give her a bow or a crossbow), as well as in opening chests and disarming traps.
Bonus for good relations to: cunning
LOGHAIN (human, warrior)
He can join your team in very unusual circumstances. During the Landsmeet quest you must defeat Loghain either in a honorable duel or in a battle with him and his men. Once he's defeated listen to Riordan's plan and agree for Loghain to go through the ritual, ignoring protests made mostly by Alistair.
Info: Loghain is a very similar character to Alistair and he'll replace him after Alistair has been killed (worst case scenario) or banished from the kingdom (best case scenario). Make sure to give him some of Alistair's things before moving on with the game.
MORRIGAN (human, mage)
She joins your team as soon as you've completed Tower of Ishal quest in [Ostagar]. This will occur during the conversation with her mother in [Flemeth's hut].
Info: Morrigan is an ideal choice for an evil character, however she's not that useful as a mage. The main reason is that she's using mostly offensive spells instead of healing the team, so you would have to change how she's being developed, rely on using potions or have a second mage in your team.
Bonus for good relations to: magic
MABARI HOUND (animal, dog)
Mabari will join your team either during your stay in [Cousland castle] (you must be playing as a human noble) or soon before arriving in [Lothering]. In this case you would have to complete a quest in [Ostagar] and wait for a random encounter.
Info: You'll definitely want to have a mabari in your team in the early parts of the game, because the animal is a great replacement to a warrior. Later in the game it's better to choose intelligent followers instead of the dog.
OGHREN (dwarf, warrior)
He joins your team soon after you've started Anvil of the Void quest in [Orzammar - Commons]. Oghren will stop you near the miner checkpoint and offer his services.
Info: I would definitely recommend having Oghren as one of the members of your team, because he's an excellent warrior. Consider choosing him even if you're playing as a good character, because he won't be offended easily.
Bonus for good relations to: constitution
STEN (qunari, warrior)
He can join your team after you free him from his cage in [Lothering]. You can do this either by relying on your lockpicking skills or by completing The imprisoned qunari quest.
Info: Sten should become a member of the team lead by an evil character. He will be very resistant to enemy attacks and he'll get even stronger if you retrieve his sword as a part of his personal quest.
Bonus for good relations to: strength
WYNNE (human, mage)
She will join your team not long after you've officially started Broken circle quest. All you have to do is to reach a larger room in [The Circle tower - Student Quarters].
Info: I would strongly recommend having Wynne in your team, especially if you're playing as a good character. She has a lot of healing spells in her arsenal and therefore she'll be every effective in saving other companions from certain death.
Bonus for good relations to: willpower
ZEVRAN (elf, rogue)
He can join your team soon after you've seen a cut-scene informing you about the threat from the Antivan Crows. Defeat him and other rogues in battle and make sure not to finish him off, because you wouldn't have a second chance of recruiting him.
Info: Zevran can be very helpful in opening locks and stealing items from various citizens of Ferelden. I wouldn't recommend using him in difficult battles, because you would have to be careful or spend money on equipping him with much better items.
Bonuses for good relations to: dexterity, strength
The table below shows my recommendations for team members depending on the class and on the affinity of the main character:
Alistair, Wynne, Leliana
Alistair, Leliana, Mabari hound (or Oghren)
Alistair, Wynne, Mabari hound (or Oghren)
Morrigan, Sten, Zevran
Sten, Zevran, Oghren
Sten, Oghren, Morrigan