You can find one of the examples here:
http://www.phpbb.com/customise/db/mod/advanced_bbcode_box_3
But I 'm sure there 's more than one mod available (possibly 3) for extending the message editor (I can not tell you what is a good one yet because I have not gotten arround to modifying this part myself yet (and I would need a good dark version, verry different form a light/white version you need)
Best thing to do is search the mod database at phpbb.com and compare the (maybe) 3 types that exist.. or post a question like TheSteffen told you!
Greetings,
...Joshua203
PS... before doing anything I would start updating your board, because looking at that screenshot ... I think you are not up to date ( phpbb3.0.8 ), or you have not fully updated