I know a lot of good DB mods, also some Thieves Guild and Mages Guild extensions.

But I don′t remember any Fighters Guild mods or extensions.

I saw this: http://oblivion.nexusmods.com/mods/41012 ,but as I read the comments it should be pretty buggy. Any other ideas?

Don't dismiss it, it's worth playing. Also http://oblivion.nexusmods.com/mods/42870/ and http://planetelderscrolls.gamespy.com/View.php?view=OblivionMods.Detail&id=4185. The latter mod is mostly cosmetic but nice all the same.

Or if you like the look and concept of JQ's Fighters Guild United but want more, you could try http://oblivion.nexusmods.com/mods/42261

Anyway, that Fighters Guild Quests mod is simply the biggest and best thing out there, bugs or not. And I haven't run across any game-breaking bugs in it personally, but I understand Oblivion can be fickle sometimes and things may not repeat exactly the same way. Best advice is to save often. And use it with Guild Advancement