The use of the term ‘dead cat’ for things that look like this, or this, on the ILAT list recently spurred me to ask for other examples of the term.
Many thanks to everyone who wrote back.* Do add further terms in the comments.
- dead cat
- windshield [Aus term]
- windscreen [US term]
- popshield
- spoffle
- fur slug (?)
- shaggy dog
- windsock, wind sock
- furball [furry ones only]
- hush puppy [furry ones only]
- mic muffle
- spit sponge
It’s interesting how many of these terms are polysemous with items that don’t really look like the a microphone cover.
*Linda Barwick, Jane Simpson, James Crippen, Aiden Wilson, Bill Poser, and Amanda Brotchie
Anggarrgoon 
I believe “dead cat” refers only the large, long fuzzy wind shields, not to spit sponges.
“Hush puppy” makes sense as a pun, but the food actually looks like the little sponge mic covers.
It’s also interesting that “windscreen” is used in the US and “windshield” is used in Oz — the opposite of their uses with the meaning “front window of a car”. I am assuming here that the Oz usage follows the UK.
I just heard “wind cover” today in a discussion about fieldwork. While verifying this via Google I got “wind muff”, “mic muff”, “wind-gag”, and “wind shroud”. Also I happened upon a “Deadcat” by Rode which shows that it’s a brand name.
I think that judging from a search for “wind microphone” the most popular terms overall are “windscreen” and “windshield”.