I forgot this one about xmag (#180712):
The manpage speaks about the "Cut" button instead of "Select". And the bug submitter also says the "bitmap" program should be replaced with "xpaint".

* xkbprint (#306708)
  - As noted in #306708, this typo in xkbprint was fixed long ago.

* xhost (#232384)
    Fixed in git master - commit 39ebc64fcc7ed7abdd529100da4cc6ba59ccff9d

* xmodmap (#236198)
    Fixed in git master - commit fd25acd688b86a1490198d61f66d2503a87883a0

* xrdb (#354923)
    Fixed in git master - commit 0b2171f2af1a5790753bb6516ac32411b1b89ef3

* ico (#395445)
    Fixed in git master - commit db38b36c535baeda5bdc8a873b32f678e7df8e36

* x11perf (#395445)
    Fixed in git master - commit ad4686b388da891ca07fba41a748ea90a3bb15cb

* various (#350313) 
     Will do soon

Here are the probably latest ones (just finished looking at all xbase-clients bugs in the Debian BTS):

* xgamma (#296021)
gamma manpage says -gamma without any value returns the current gamma value. It actually does that when no option at all (even -gamma) is given.

* startx and xinit (#267744)
startx manpage should document that "display must be the FIRST server argument" as documented in the startx script (the xinit manpage does that).
xinit manpage should have "..." to show that multiple argument may be given (as the startx manpage does).

* setxkbmap (#252631, already reported as #7841)
some options are given in -help but are missing in the manpage: -device -I -keycodes 

* xev (#265594)
should document how to quit if it exists (need to ctrl-c or kill?)

* xev (#269410)
document what the black square is here for

* xrdb (#59308)
doesn't seem to support spaces in the argument that is passed to -I, this should at least be documented...

(In reply to comment #3)
> * setxkbmap (#252631, already reported as #7841)
> some options are given in -help but are missing in the manpage: -device -I
> -keycodes 

Fixed in git master - commit ca1e9f1cc9716a0cb751853cfb7b6b0ff6bb21d6 

> * xev (#265594)
> should document how to quit if it exists (need to ctrl-c or kill?)

Doesn't look like there's anything to document here -- there is no exit 
method I see in the code - just close the window using
your window manager or kill/Ctrl-C it.    

> * xev (#269410)
> document what the black square is here for

Not sure how to describe this for non-X-hackers - it's so you can see
EnterNotify/LeaveNotify events.

> * xrdb (#59308)
> doesn't seem to support spaces in the argument that is passed to -I, this
> should at least be documented...
> 

Seems like a code bug, not a documentation error.

Thanks a lot Alan! To summarize, only the following ones are remaining:

* various (#350313) 
have all the following manpages refer to each other in SEE ALSO:
      xprop xvinfo xdriinfo glxinfo xwininfo xdpyinfo
(old patch available at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=350313)

* xmag (#180712):
The manpage speaks about the "Cut" button instead of "Select". And the bug
submitter also says the "bitmap" program should be replaced with "xpaint".

* xgamma (#296021)
gamma manpage says -gamma without any value returns the current gamma value. It
actually does that when no option at all (even -gamma) is given.

* startx and xinit (#267744)
startx manpage should document that "display must be the FIRST server argument"
as documented in the startx script (the xinit manpage does that).
xinit manpage should have "..." to show that multiple argument may be given (as
the startx manpage does).

(In reply to comment #5)
> * xmag (#180712):
> The manpage speaks about the "Cut" button instead of "Select". And the bug
> submitter also says the "bitmap" program should be replaced with "xpaint".

Fixed the button name in xmag.man in git commit bff2deea15bd0b676458b88acb46d63fd72b86af - left "bitmap" instead of "xpaint"
since X.Org only provides "bitmap", not "xpaint".

> * xgamma (#296021)
> gamma manpage says -gamma without any value returns the current gamma value. It
> actually does that when no option at all (even -gamma) is given.

Fixed in git commit 52251cd5c6e70a1cc3b037e976da4c8a7d8d4d5b.

> * startx and xinit (#267744)
> startx manpage should document that "display must be the FIRST server argument"
> as documented in the startx script (the xinit manpage does that).
> xinit manpage should have "..." to show that multiple argument may be given (as
> the startx manpage does).

Fixed in git commit 3b6dad2ba4d4507cd742d8e7ff760fe006c0aa23 in app/xinit.

That leaves this one last batch to do soon:
> * various (#350313) 
> have all the following manpages refer to each other in SEE ALSO:
>       xprop xvinfo xdriinfo glxinfo xwininfo xdpyinfo

(In reply to comment #6)
> That leaves this one last batch to do soon:
> > * various (#350313) 
> > have all the following manpages refer to each other in SEE ALSO:
> >       xprop xvinfo xdriinfo glxinfo xwininfo xdpyinfo

All done now except for glxinfo, which now lives in Mesa, not X.Org sources.