Please only add tests that are really acting random and cannot be simply fixed.
Updating the list
Testman fetches the current version from the SVN repo. To update the blacklist, checkout testman from svn://svn.reactos.org/web/trunk/www/www.reactos.org/drupal/sites/all/modules/reactos/testman/, locate and update blacklist.txt and commit.
dinput:mouse gdi32:mapping kernel32:loader kernel32:mailslot msi:msi msxml3:domdoc ntdll:info - number of tests/failures depends on the number of running processes which may vary between runs quartz:referenceclock shell32:appbar urlmon:url - (Alex: is wildly random/erratic, I believe due to ws2_32:sock) user32:menu user32:msg - random possibly due to TrackMouseEvent
user32:win - number of tests/failures is quite random wininet:http ws2_32:sock