Jeykl and Hyde Syndrome by ~RumblingGear on deviantART
Here's an absolutely gorgeous breast expansion, butt expansion and general-hotness-enhancement montage from RumblingGear at deviantART.
I found a delightful breast expansion story at the BE Story Club called "Accidental". Written by "Gunslinger", "Accidental" is about four college women who, following an automobile accident, encounter some strange chemical storage drums in the woods. In the hours following the crash, each discovers that her breasts are slowly (or rapidly, depending on your time perspective) growing larger. Much, much larger!
Although flat-chested Jen is at first delighted to find her formerly small boobs growing to spectacular proportions, even she begins to panic when they just keep growing! And the other three already had decent-sized or big breasts already! How huge will their tits grow? You'll have to read the story to find out!
A flat chested student goes to bed after working on her science fair fungus project, only to wake up the next morning with enormous breasts and a cup size in the second half of the alphabet! "Where did these come from?!" she asks, astonished at her staggering rack.
But it doesn't stop with her! Within a day or two all the girls in school are experiencing rapid, massive breast expansion! Somebody call the CDC, because there's a big-tit epidemic!
Fortunately for our protagonist, her direct exposure to the fungal spore causes her to keep growing, bigger and bigger, and no one else even comes close to her eventual, supremely big titted proportions!
That's the plotline from Spore, a comic available for digital download from the BE Story Club. Growing tits forever!
In one episode of "Charmed", Rose McGowan's character had an accident with a spell and wound up with gigantic breasts. Warning: this video has a very sad ending!