Silver-Tongued Devil

Silver-Tongued Devil is an achievement/trophy in Fallout 3.

Requirements
Pass 50 speech challenges.

Vault 101
There are not many speech challenges in the vault, but be sure to save Amata before taking the G.O.A.T. Then tell Butch to run away from his mother (since it has a higher chance). After escaping Vault 101, be sure to get the speech challenge from Silver who lives in small ranch between the Vault and Springvale School. Even if you're not really interested in the money she gives you, you could always execute her afterwards.

Megaton
There are several non-player characters in Megaton that present speech challenges: Lucas Simms, Jericho, Doc Church, Mr Burke, Gob, Colin Moriarty, Leo Stahl (the player will need to win Doc Church's speech challenge before they can do this one). It is possible to lie to Moira Brown multiple times during The Wasteland Survival Guide quest, though much less loot and perhaps a lost perk will be the result if too many lies are told. The player should also take care not to talk Moira out of finishing the guide, unless he/she wants to receive the Dream Crusher perk.

Blood Ties quest
This quest is fairly quick and has plenty of speech challenges. After getting the quest from Lucy West the player can get a speech challenge from Evan King in Arefu. There are also several speech challenges in Meresti station.

Tenpenny Tower quest
This is a gold mine for those trying to get this trophy/achievement. Tenpenny Tower has many non-player characters offering speech challenges. No matter your choice (to help or kill the ghouls) you can get a speech challenge from Gustavo, as well as the five people on Tenpenny's list.

Rivet City
There are 4 speech challenges involving a rumor mill with Vera Weatherly. This one in particular is useful as it can be repeated over and over until the achievement is earned.There are also a handful of them to do with The Replicated Man quest. There is one with Dr. Madison Li which will get you five stimpaks once you talk to her about Dad. There is one with Abraham Washington concerning the Stealing Independence quest.

Oasis quest
There are a handful of speech challenges when doing the Oasis quest.

Republic of Dave
There are three speech challenges when doing the Election Day quest.

Paradise Falls
The Rescue from Paradise quest has few speech challenges:
 * 1) Try to buy your way into Paradise Falls at the front gate;
 * 2) Persuade Eulogy Jones to sell the children to you for fewer bottle caps;
 * 3) Persuade Grouse to give you another slave collar for free after one of the slaves you enslaved are killed before they reach Paradise Falls. This can be done once for every dead slave.

Little Lamplight
Convince Bumble in Little Lamplight to leave the cave and go with the Child Slaver Note: You will need to speak with Eulogy Jones before going to Little Lamplight to get this quest.

Knock Knock can be used to easily unlock the Silver Tongued Devil achievement. Talk to her and ask her about morale, then get her to tell you a joke, play along then you'll get a speech challenge. This challenge is repeatable as many times as you wish. Repeat it until you earn the achievement. This is probably a bug/glitch. Still works even after patch.

Canterbury Commons
During The Superhuman Gambit, there are many speech checks available in dialogue. Note: Using the Black Widow perk, the Lady Killer perk, or the Child at Heart perk may prevent the player from accessing some of the challenges on this quest.

Girdershade
During The Nuka-Cola Challenge, the player can engage in a few Speech checks with Sierra Pertovita. The player does not need to complete this quest to get all of the speech challenges.

Jefferson Memorial
Take it Back!, the last quest of the game, offers two speech challenges when you meet Colonel Autumn for the final showdown at the end.

Underworld
You Gotta Shoot 'Em in the Head has many speech checks for players wanting less violent ways to accomplish the quest. All told this quest has 19 possible speech checks, the largest of any single quest.

Vault 112
Complete the Tranquility Lane Quest with the bad karma options to unlock several speech checks.

Lincoln's Profit Margins
Finding Abraham Lincoln items in the Museum of History allows you to sell them to Hannibal Hamlin or Leroy Walker. When selling each item, they will offer you some caps or double when passing a speech challenge ( see Lincoln's Profit Margins). This could net up to 8 speech passes although you may want to hang on to Lincoln's repeater.

Big Town
Pappy in Big Town has a speech challenge. Simply talk to Bittercup so she will tell you about her boyfriends, then go to Pappy for the challenge. Repeating it will net you XP and get you closer to the Silver-Tongued Devil achievement/trophy.