The list on the wiki is exhaustive as far as I'm aware -- there just aren't that many tiles you can change. The only tiles you can change are the ones marked with *, # and $. Combined with the fact that you can only use one tileset with 256 tiles (
the tileset), a big problem is certainly that many tiles are used for multiple things and changing these tiles will have to be some sort of compromise. E.g., you can make the 'X' look like really good up/down stairs, but then the cursor, wooden bins, and the letter 'X' in text will look like stairs too.
There are also creature graphics of course. See here for more information:
http://dwarffortresswiki.org/index.php/DF2014:Graphic_setQuiet-sun wrote a set of utilities to automatically generate text files for creature graphics:
http://www.bay12forums.com/smf/index.php?topic=156151.0I also find BradUffners "Raw Explorer" especially useful for checking a creature graphic set for completeness and finding problems/errors in your text files.
http://www.bay12forums.com/smf/index.php?topic=103360As it's been mentioned there's a third party utility called "Text Will Be Text", which - with DFHack - allows you to assign more tiles than possible in vanilla. Especially the problem that tiles get used for several things I mentioned above is solved with that. It's probably your best bet if you want to avoid the current (as in "the next 20 years") limitations of Dwarf Fortress' graphics.
PS: It doesn't hurt to check this list:
http://www.bay12forums.com/smf/index.php?topic=28829.0There might be some utilities which are useful to you as well.