From very old median builds, such as aerial's mentioned.
Judgesin (M2008): very strong farming build that utilizes level 17 runeword (CtC Thunder Hammer on striking) and bunch of crafted jewellery with similar effects. It was very strong because Hades Gate had extremely long range, way past a screen's reach when maxed.
The Invincible Barb (M2008): yeah, this one was more for show and for clearing harder uberquests which does not really require speed. Also very cheap to make, utilizes two TIERED uniques: Darkspite (CtC Unholy Armor when struck) and Razorscale (CtC Spike Nova when struck - yeah, you also need to do damage, not only be immune to it). Basically it was like socket as much buff / debuff as you can (there was a cap but it was high), then use Conquest (level 24 barb skill) which is 6 sec invincibility. Then, during these 6 sec you get hit a lot, which triggers UA proc - a much longer invulnerability shield. Then you just get hit alot, triggering more UA and killing stuff with Spike Novas and whatever damage stance you're using.
Apoc/STF Sorc (M2008): also overpowered due to extreme range on those spells. Median XL fixed those issues and limited the range on most stuff like that. In Median 2008 the range was like 70 yards, so you just spammed Apocalypse and exploded the corpses with STF. You rarely seen a living monster. It was easy to hit damage cap in Median 2008, as you had 10 stats per level up and items were very strong.
Tempest sorc (MXL): this was really OP when Tempest had uncapped amount of bolts and could reach 25+ with good gear. Nowhere near truly broken builds but i had such sorceress and it was very good at clearing TA.
Dfzon (MXL): yeah this one was OP as well, DF was nerfed multiple times, at first it had like 5 attacks per second, after nerfs just 2 or 3. An even stronger weapon for this character was realm bow "Vizjun's Scitek" which had a ridiculous CC proc (it was this assasin piercing icebolt, forgot the name). This thing froze everything AND it had like 6k elemental damage on it (that's like a maxed Way on an assasin).
Proc spam waysin: tons of variants of this build, my favorite was using a RW bow (40% CtC Arrow on striking) together with untimered Wyrd oskill. This was an unorthodox assasin becasue she didn't use any assasin attacks except queen of blades to generate even more arrows. Just wyrds that nicely cover a wide area and produce a massive arrow spray. Damage off passive ways ofc, all the skill points went there because you really didn't need any other skills.
A fun build but not sure if even possible now: Hermanubis druid.
Uses the great RW of the same name, which gives alot of fast-moving zombie reanimates. Then you made those reanimates melt face with pet commands (such as killer instinct which gave them a boatload of damage). Druids no longer have pet command tree so this build is basically dead.
Also there was a time, when signets of learning didn't had any cap on them. You could pump the stat points up to whatever the game engine allowed (it was like 8191?) Obviously this was a bit silly. IDK if anyone actually reached 10k+ signets but with a fast build it wasn't a huge grind to get like 2-3k extra stat points (which was many times more than your leveling stat points and obviously unintended).