Here is another plug for writing tag wiki's.

We still have several tags on the first page which have no wiki at all, and nearly anyone can suggest a edit for them. (And on approval you get the usual 2 points for a good edit.)

Remember there is a badge for that.

Open topics include "astrophysics", "electricity" and "energy"!

Also I am sure that many existing tag-wikis could use some effort.

Most of the time, when I post this suggest I go through a write a few words about some tag or another, but unless I'm an expert I generally only write a stub. The result is a bunch of wikis which exist, but could really use some improvement.