You're quite right, I'll bring it out here to try and keep the rest on-track.
Actually, the first is in the SRD (Improved Unarmed Strike) and the second is in Tome of Battle, which was written and published by WotC, so by no means third party. That said, Tome of Battle is widely reputed as being overpowered (much like every other 3.5e splatbook), but "Superior Unarmed Strike" isn't why. In fact, most DMs I've played with have disallowed everything in that book except for that feat.
From an optimisation standpoint it's actually one of the most balanced books Wizards ever managed to produce, oddly enough. A lot of the cries of "overpowered" stem more from the idea that "Fighters can't have nice things" or knee-jerk reactions to abilities that look impressive but ultimately work out rather modest, mathematically speaking, than any real case of overpowering.
One expects the same people to consider the Monk overpowered, as backwards as the notion is considering the 3e monk is one of the worst in the edition.@ZanathKariashi
Improved Unarmed Strike is no more, no less than any other Weapon Proficiency feat, if you're non-proficient with a weapon you take -4 to hit, if you're non-proficient with your fists, you take -4 to hit to deal Lethal. It's only marginally less useful than Exotic Weapon Proficiency - Bastard Sword.
Why, may I ask, do you consider the ability for a level 20 character to deal 2D6 damage with an unarmed attack to be an "OP piece of garbage"? Superior Unarmed Strike, unless you're at least partially monk or Unarmed Swordsage, means you theoretically can't pick up Improved Natural Attack feat to up your die size, so it works out quite reasonable.
Also of note for making a viable, non-Prestige/non-Monk brawler in 3e are Snap Kick (Bo9S again), which allows an additional unarmed attack on a full attack for a -2 penalty to all attacks that round; and Versatile Unarmed Strike (Player's Handbook II), which simply allows you do pick if your unarmed strike is piercing, slashing or bludgeoning.
Neither of these really raises a blip on the optimisation meter, they simply exist to make unarmed combat viable. Considering for the same opportunity cost of 3 feats you have Melee Weapon Mastery for +3 to hit, +4 to damage with a particular type of weapon (and +2/+2 to all weapons which share the same damage type as that weapon), and sneak in Slashing Flurry for an extra attack just the same.
Concerning Enhancement, the Amulet of Mighty Fists is Core and improves all unarmed strikes by its enhancement bonus, whilst the Necklace of Natural Attacks from Savage Species does much the same. It's the ability to attach a +1 to a Gauntlet and then make it Flaming, Acidic, Holy and Shocking whilst using the superior enhancement bonus from the amulet or Improved Nature's Fang that helps bring unarmed to almost the same level as other weapon choices.