Buffout and X-cell temporarily increase Strength by 2, giving 20 extra carry weight.
Lone Wanderer increases carrying capacity by 100 when not traveling with a companion (except Dogmeat).
Strong Back increases carrying capacity by up to 50, and also counteracts some of the deficits of being overencumbered by offering the ability to run normally or even fast travel.
Movement speed is unaffected by carry weight unless overencumbered, and one is unable to run or fast travel, but can still jump.
With the Long Haul perk in Fallout: New Vegas, one can still fast travel while overencumbered.
Using the console command player.modav, carry weight can be increased to a maximum of 20,106 lbs.
In Fallout: New Vegas, the maximum amount of weight one can carry is 400 lbs.
The NCR Courier duster increases carry weight by another 25 lbs.
The Hoarder trait increases the limit by 25 lbs.
The Burden to Bear perk can increase this limit by another 50 lbs.
The Strong Back perk increases the limit by 50 lbs.
The maximum initial level is capped at 250 lbs without the addition of extra perks.
Every added point of Strength increases weight limit by 10 lbs, including temporary bonuses added from chems, alcohol, and apparel.