Dr. 8, if the player has a high enough Perception of 7 or Intelligence they can understand him. If the player has a Science skill of 75 they can program him to mindlessly do what they want.
Dr. Borous, with a high enough Speech skill the player can talk to him about the fact that his experiments have escaped the Big Empty and into the Mojave, although he refuses to believe it.
Dr. 0, if the player has an Intelligence of 9 or higher or the Math Wrathperk, the player can work out his real name is "Dr. Zero".
Dr. Klein, by following various dialogue routes and having a good level of the Medicine or Science skill, the player can gather info about the other courier, Ulysses, and Father Elijah.
Dr. Dala, if the player has a high enough Medicine or Charisma or the Cherchez La Femme perk, they can work out that she misses her body and secretly has some sort of fetish for teddy bears, which can be used to complete her portion of the quest. Teddy bears can be obtained in Dr. Dala's room on the 2nd floor of the Think Tank.
Talk to Dr. Klein, despite your lack of earmuffs.
Chat with Dr. O.
Introduce yourself to Dr. Dala.
Say hello to Dr. Borous. Carefully.
"Speak" to Dr. 8 - if you can.
By picking the right response with each Think Tank, you can get extra supplies and caps.
Picking the correct response when talking to Dr. 8 can gain you some good Karma.