So When I went across the Fallout 3 Nexus i came across some awesome companion mods, and the mods gave me an idea for an interesting mod request to add some companions. what I'm thinking are some NPC's from the Capital and Mojave, but i'll start with the Capital.
Amata (Req Neutral, good, Very good karma): After you complete the "Trouble on the homefront" quest, Amata is appointed overseer, but instead of kicking you out, Amata can be convinced to appoint the position to someone else (or make a democratic process, or something), and decide to travel with you through a speech check, and she'll you the nearby Ranch house (silver lives there) as her Dismissal point or something
Lt. Williams (reqvery Evil, Evil Karma): after you leave your cell, and you can talk to Williams who will try to stop you, if you do any other option that doesn't kill this guy, he'll be discharged and kicked out of the Enclave, and find a new home, (Near paradise falls or something), so how he is discharged is if you bride him overhears it and discharges him, or if he interruptsyou and messages Eden to check, he is Discharged for interfering with Enclave high affairs
Rory Maclaren (Req Good, Very Good karma): After you get that poor bastard out of the box, should he survive, he'll Head to Megaton and Work for Moriarity(the bar owner), and if you have a high enough explosives you can take off his collar, and would join you if you pay off his debt to Mariarity as well (like 100 caps or something)
Dave (reqEvil, Neutral, Good karma): After you have the vote for a new President in the Republic of Dave, and you get other people to run as aPresidential Candidate you rig it so Dave loses, and instead of Having him go into Old Olney and get killed by Deathclaws, you convince him to join you to start a new republic elsewhere.
Burke (req very evil, evil, neutralkarma): After you blow up Megaton Burke joins you as a companion as your personal servant for Mr. Tenpenny, or rather if you are a female Character, you can use the Black wido perk to convince him to spare megaton, and you meet him at tenpennytower, and he'll willing join you
Sydney (no karma requirement): After you complete the "stealing independence" you can convince her to keep traveling with you, through the gun nut perk, a speech check, or other means, and also if you give her the news about her father, and gives you her gun, she'll you a regular 10mm SMG
Herbert Dashwood (req Nuetral/good/verygood karma): After you head to Rockopolis, you come across Argyle dead body, and if you head to Tenpenny tower, you hear Dashwood'sstory of his adventures, and you tell him Argyle's fate, and instead of having Herbert go into retirement as an adventurer, you convince him to go on an adventure with you.
Gary {insert random number here} (no karma requirement): So... this Gary Clone isn't insane as the rest, he'd be willing to join you since he wants to see the world of Non-Gary, and by doing so he'd be willing to travel with you since the other Gary's casted him away as being non-hostile towards non- Gary peoples (hired outside vault 108's vault door, in that cave area, but if he's dismissed he'll go to Tenpenny tower or something)
What I also think is that if someone would be awesome enough to make this, the maybe add companions to the Mojave? I have some ideas that I'll post below if anyone is interested. (not adding karma requirements since Fallout NV focuses on reputation more than karma)
Boyd: after you help her with the Centurion situation, you can talk to Hsu (who is her commanding officer) and get him to station her as your personal NCR Bodyguard, or for legion player you can convince her to go AWOL and help you through a speech check, or maybe enslavement?
Beagle: after the completion of "my kind of town" beagle is out of a job, and he'd be willing to join you after since he has nothing better to do in primm, and he'd join you because you did save him afterall.
Vuples Inculta: Once you reach the Fort, Caesar Gives you Vulpes as your personal legionnaire after you destroy House's bunker (or so he thinks). He will be willing to join you as well as abandoning his legion title and slay the fort through a really high speech check (for the non-legion players).
Siri: Now I always felt bad for her being a slave. So my idea is, if you become friends with the Legion Caesar gives you her as well as a gift for being accepted among his people. She doesn't care if you kill the legion because she will bluntly state she wants to leave.
Blade: The marked man who you kill before you meet Ulysses in the Divide. My thinking for this is, if you kill the three other Marked men, Blade will see you as one of the Strongest marked men, and will meet you, even though all he can do is growl and moan (like a feral ghoul). you understand he's trying to join, and your given the option to hire, deny him (in which he will wait for you to say yes or until you have no companions), tell him to head to the 38, or kill him as the marked man he is.
Sunny Smiles: this is pretty self explanatory, but after doing the tutorial and the "Ghost town gunfight" quest, if Sunny survives, you can recruit her to join you, and Cheyenne,
Benny: Surprised I'm saying that name? so am I, but what i'm thinking is, after you deal with houses bunker Caesar demands for you to deal with benny, but if you free him you never see him again, so what I am think is instead of freeing him, you helphim escape and you meet him somewhere else, and he'll join you from there
Melissa: After you help her with her Khan Drug Problem and don't report her or her father. She'll join you and will keep traveling with you should you not be shunned by the khan's, as a survivalist and chem dealer companion.