Something from the Premodern Japanese Studies List: the Hyakugo Archives, or "Archives of Toji Temple Contained in One Hundred Boxes Online" as they call themselves. (Hyakugō 百合 = "Hundred" + the counter word gō, presumably applying in this case to boxes because 合 means "come together" and can be used to count things with a lid.

Interestingly, according to Wikipedia, the archives don't actually contain one hundred boxes, and never did, either. Quick translation:

Before the beginning of the Edo period [1603 - 1868], Tō-ji [temple]'s documents were stored in leather bags and boxes of various kinds. Tradition says that in 1685, when Kaga daimyō Maeda Tsunanori 前田綱紀 copied the temple's document collection, by way of thanks he not only created a catalog of the documents before returning them, but also had them put into one hundred specially made boxes of paulownia wood with the hiragana and katakana (in iroha order) and the character 京 ("capital", i.e. Kyoto) on them. However, as there are presently only 94 boxes, and in any case the total number of hiragana plus katakana plus the character "京" falls short of 100, whether the Kaga domain gave the temple 100 boxes of which some were lost or whether 100 should be viewed as an approximate number has been considered a mystery. In 1997, on the occasion of the exhibition "The world of Tō-ji's 100,000 documents" 東寺文書十万通の世界 at the Tō-ji treasure house 東寺宝物館, investigations led by Uejima Tamotsu 上島有 revealed that Maeda's offering to the temple was originally 93 boxes and that the 94th was a later addition made of a different kind of wood (momi fir). In any case, the original belief that there were 100 boxes led to these documents being known as the Tō-ji Hundred Boxes of Documents 東寺百合文書.

(If there were originally 93 boxes, then that makes 46 each of katakana and hiragana, plus one 京. But the Iroha poem has 47 characters, so I don't know what's going on there. If you browse the boxes by character you will observe the necessary omissions but I see no pattern to them; perhaps Uejima's work explores this.)

Not gonna lie, using this site to do meaningful historiography is beyond my current form, but pretty much anyone can enjoy the stories they post explaining some of the context behind the documents. Also, the terms are fantastic: virtually everything is provided under a "Creative Commons Attribution 2.1 Japan License," which as I understand it means you can do whatever you like with it as long as you credit the source.

2015-10-14 update: Light edit for readability.