It's amazing sometimes how much there is to learn. Earlier I was looking briefly at today's copy of the 日経新聞 (the Nikkei) and I noticed one of the headlines contained a non-kanji character I wasn't familiar with. The word was 「いすゞ」。
I asked one of my coworkers, and it appears I discovered the hiragana version of 「々」. This character is used to indicate repetition of the character before it. For example 「色々」is another way of writing 「色色」。
According to my research, these things are called 「踊り字」or 「繰り返し記号」, though you can call them up by simply typing 「くりかえし」and scrolling through the kanji choices.
Apparently there are separate characters for use in hiragana, katakana, and kanji:
Hiragana - ゝ (or ゞ)
Katakana - ヽ (or ヾ)
Kanji - 々
As you can see, unlike their kanji kin, the kana versions can be accented to represent a change in sound, just like normal kana (though the little circle versions don't seem to exist).
Learning something like this now makes me feel a little noobish, but at the same time it's gratifying to know that there are still simple elements of Japanese like this out there for me to discover.