I am familiar with Yotsuba and Totoro, but who is the third character in this picture (the one in pink) ? What manga/anime is she from?
It comes from some desktop background site which sadly did not give any attributation to what is obviously fan art.
She's from Hare+Guu, or "The Jungle Was Always Sunny, Then Came Guu".
It was originally a serialized manga that was then adapted into a 26 episode anime TV series as well as several OVAs.
She's one of the main characters and her name is "Guu".
Here's some more information about the characters, and specifically, about Guu:
Guu's stomach is a world filled with buildings, hundred legged cats, and a nice young couple of lovers that have been trapped there for ages (but apparently don't mind their predicament). Other than Haré, no character seems to be aware of Guu's strange nature (or for that matter the bizarre circumstances surrounding everything else in the series). The weird events that occur because of her are only ever acknowledged by Haré. Everyone who is eaten by Guu, only to be spat out later (excluding Haré) dismisses what happened as "sleeping" (occasionally, dreaming about Guu's Stomach world). Haré even dismisses his first time in Guu's Stomach but is quickly proved wrong. There are other strange things Guu can do, which defy the laws of physics, logic, and reality, such as (but not limited to) teleport, time travel, warp reality, superhuman strength, elongate her body parts, breathe underwater, cause people to switch bodies, read minds, cause disco music to play suddenly, switch her face (from a cute face to a completely plain face), transform into a giant kaiju monster version of herself, and incite mental breakdowns in Haré, though the latter is more of a talent than an actual power. She apparently has more than one stomach and cares enough about the people and creatures she swallows to keep dangerous things away from the area she keeps her 'guests'. Despite all this, Guu actually cares for some of Hare's personal problems, and often gives him advice with profound sayings- a lot of her powers are used to make Hare learn a lesson. At the end of the manga, Guu leads Hare to her birthplace in a dream (and refuses to let him go further, saying it would be an one-way trip for him), and it's strongly implied that Guu's birthplace is somewhere between life and death, and that she's some kind of physical god. Guu disappears the next morning, releasing the people in her stomach (who turn up in a TV shows about missing people suddenly reappear) and erasing everybody's memories of her, except Hare's. Six years later, Hare spots Guu's smirk on his newborn daughter's face, and realizes she might be a reincarnation of Guu.
