I find this thread interesting in part because of the debate to define balance. That's a tough starting point.
I think that what's been discussed hits a few key highlights.
1. A product that exceeds the 'average' or 'comparable' damage, defense, or ability of an existing core rules model.
2. A product that affected the level of enjoyment of the players or DM.
Both of these balance tests are quite subjective. I often think that there are some who are better at identifying and exploiting balance questions, and that to these people the 'obvious' balance issues (as illustrated in point 1) are overlooked in products.
My personal experiences that meet this criteria are largely front-loaded from the last five years as most d20 pulishers have gone away or stopped releasing 'add-on' content. I could highlight several experienced including Relics & Rituals, R&R2, Rokugan, BoEM, and so on. I could also site as many examples from WoTC material however including the Dervish, Mystic Theurge, an Archer, Vorpal Swords, the Templar, a Mantle of Mind Blank, touch attacking rogues, slimewaving a tarrasque, and Red Wizard/Archmages.
I think that what's been discussed hits a few key highlights.
1. A product that exceeds the 'average' or 'comparable' damage, defense, or ability of an existing core rules model.
2. A product that affected the level of enjoyment of the players or DM.
Both of these balance tests are quite subjective. I often think that there are some who are better at identifying and exploiting balance questions, and that to these people the 'obvious' balance issues (as illustrated in point 1) are overlooked in products.
My personal experiences that meet this criteria are largely front-loaded from the last five years as most d20 pulishers have gone away or stopped releasing 'add-on' content. I could highlight several experienced including Relics & Rituals, R&R2, Rokugan, BoEM, and so on. I could also site as many examples from WoTC material however including the Dervish, Mystic Theurge, an Archer, Vorpal Swords, the Templar, a Mantle of Mind Blank, touch attacking rogues, slimewaving a tarrasque, and Red Wizard/Archmages.