Many people seem to be looking for the relation of these stories with the Hollywood movie Avatar. While I've not seen the movie, here is what I know of the subject - along with download links I know of.
"Avatar" & "Call Me Joe".Folks are finding the telepresence aspects of Avatar a lot like Poul Anderson's short story "Call Me Joe".
In Anderson's story, no human can go to the world that needs exploring. So they create an artificial animal that can thrive in that environment, but is otherwise like a baby. Mind of this artificial being is linked by a communications link to that of a man elsewhere (an invalid, a few million kilometers away). Man can become one with the artificial creation by pressing on a button.
Note there are at least two other well known short stories with similar themes: Clifford D Simak's "Desertion" & James Blish's "Surface Tension". No communications link is involved in these two stories.
In Simak's version, you put a man in a machine, & out comes a being physically adapted for the hostile world, but with the mind & memories of the man who entered. Process is reversible. So the machine can take the local being with his local experiences, & turn it into the original man but with additional memories of his experiences in this artificial body.
In Blish's story, a few human embryos need to be left on a hostile world, with no adult to take care of them. How do you ensure the babies that these embryos will become can survive on their own? You turn them into locally adapted animals but with human minds. Very colorful story - probably the best known short work of Blish.
I know of at least 2 online versions of "Call Me Joe": an audio, & a comic book adaptation.
Text of "Desertion" is included in the scans of the whole Astounding issue where the story originally appeared.
MP3 audio of "Surface Tension" is online.
"Avatar" & "Midworld".People are finding the alien world of Avatar (& some of its creatures) rather similar to Alan Dean Foster's novel "Midworld".
"Midworld" features a jungle world - a semi-sentient jungle with huge trees that have 7 vertical levels - each level offering a unique ecological niche. Humans live in, I think, level 4 - hence the title. Moving across levels means inviting death - though humans often go through these adventure.
Note that "Midworld" itself is a rehash of Brian W Aldiss' "Hothouse". "Hothouse" has at least two versions - an original short story version, & a later novelization (I've only read first third or quarter of this novelization).
"Hothouse" is really a juvenile work - at least the novel version. "Midworld" is a work for grown ups.
A few months back, BBC had done a show or a podcast based on "Hothouse" - I'm not sure which version. I don't know if it's still available at their web site.
"Hothouse" short story version is probably old enough to have its text online somewhere, but I don't have the URL.