Easy answer: Literally whatever you want.
Better answer: Most off-meta builds involve mixing and matching generic power boosts in secondary or tertiary talent trees. It doesn’t make much sense to dip into Balance at all as a Feral since you can’t get any useful talents in 99% of them that can be used while in Cat or Dire Bear Forms. However, for classes like Priest and Paladin, there are options that exist that let you try to focus on a particular spell or class theme.
Example 1: Pure Smite Priest
https://tbc.wowhead.com/talent-calc/priest/0550100130505102501-005551002020052
Idea behind the build is to Smite spam with Holy Fire, and it captures the relevant synergy talents of Force of Will and Spiritual Guidance. This build isn’t meta though because it offers none of the utility of a Shadow Priest, would have to nerf itself further to get things like Improved Divine Spirit, and goes OOM really really fast.
Smite Priests do better by getting more focus into Shadow to amp up SW:Pain and SW:Death… but at that point you’re just an anemic Shadow Priest who uses Smite instead of Mind Flay and Mind Blast, and minus the utility to make it that much better.
Example 2: Vengeance Protadin
https://tbc.wowhead.com/talent-calc/paladin/-0500503350000130501-0500505130030125
The idea here is that you trade a ton of survivability in favor of a lot more damage output while relying heavily on Consecration for your damage output. This isn’t really super workable in raids like T5, but probably can be used in some Heroics with the right gear and definitely a lot of Normals. The real bright spot for this build is that it is a farming build, like Stratholme or Black Morass or whatever it is you enjoy AoEing down. Vengeance procs fairly regularly despite not prioritizing any Critical Strike Chance, and Consecrate does a ton of damage thanks to all the modifiers you’ve added to it, letting you focus almost entirely on being unhittable (only Blocks, Dodges, Parries, or Misses) and having enough Block Value that you barely take any damage.
The takeaway is that most of the “creative” builds are just things like above with minor variations. Some classes are more prone to having alternatives than others, notably classes where you don’t entirely change roles from talent tree to talent tree, but that’s all there is to it. Every now and then an off-meta build will rise up because it actually competes quite well. Kebab Warriors (that is DW Arms Warriors) is one such example, with Kebab scaling very well, being easier to play than traditional Arms, doing comparable damage to traditional Arms, and still bringing all the debuffs/buffs that Arms is brought for in the first place. All it does is dip into Fury more deeply to grab different damage bonuses that work with DW.
Beyond that you really only have oddball gearing setups, like SP Hunters trying to make their minimal magic damage hit much harder… because reasons I guess?