What do you mean by Spongers? Dictionary.com says it's a parasite.
Bullet Sponges.
Those new DLC enemies that have about 2-3 times the health the enemies from the orignal game have, that also hit harder then said orignal enemies.
Examples:
Fallout 3: Feral Ghoul Reavers, Swampfolk, Tribals, Aliens
Fallout New Vegas: Lobotimites, Robo-Scorpions.
My List:
Loot: Honest Hearts, .45 Auto Pistol and SMG are some of my favourite guns
Story: Dead Money
Challenge: Dead Money
Bullet Sponges: Old World Blues
Location: Old World Blues, I liked the places of Big MT. The enemies, not so much.
I haven't really played Fallout 3 since New Vegas came out. That's why I don't have any of the Fo3 DLC's listed.