Through an interesting Language Log post (“Semen, green rice and the rate of internet decay”) by Mark Liberman, I learned about the Unihan site (it was actually mentioned in the comments to this LH post from last year, but there was so much else being discussed I didn’t even notice it). The search page allows you to search for characters by meaning or transcription, the latter in “three varieties of Chinese (Cantonese, Mandarin, and Tang), the two basic Japanese pronunciations (Japanese On, or Sino-Japanese, and Japanese Kun, or native Japanese), and Sino-Korean,” and the radical-stroke index allows you to look them up as you would in a traditional dictionarly. And the results page, eg for ren2 ‘man(kind), people,’ gives you not only its number in the most important dictionaries, readings in the six varieties mentioned above, and definitions, but a long series of phrases using the character in both Chinese (Mandarin and Cantonese readings) and Japanese (kanji and kana).
One problem is that if you search by meaning, what you enter is treated as a string of characters rather than a word, so that entering “man” gets you 355 matches, including characters with “manifest,” “manner,” “womanly,” “command,” and so on in the definition. There’s probably a way around this, but adding spaces before and after doesn’t work.