Chinese Calendar Online: Resorces relating to the Chinese lunar calendar (农历 nónglì). You can see today's date, convert days, learn the basics of the lunar calendar, and learn the dates of traditional holidays. Available in English and Traditional Chinese.
Chinesenewyear.net: lots of information about Chinese astrology, holidays, and traditions.
Eating China: read about Chinese food history and culture and find recipes in English.
Phonemica: a large collection of recordings from different Chinese-speaking regions around the world, in which contributors add recordings of "regional lore, nursery rhymes & childhood games, preparation of local foods, humorous anecdotes, local history," and more. You can use it to hear the sounds of different accents and dialects based on region.
Asia Society: organization covering and analyzing Asian politics, art, education, and more (not just China specifically).
OutChina: LGBT stories and resources from China. They have a lot of cool resources, including a podcast in Mandarin and a YouTube channel about the social issues regarding LGBT people in China. Bilingual in English and Simplified Chinese.
Mandarintools.com: there are several tools helpful for learners on this site, including language learning plugins, money conversion tools, a way to repair corrupted Chinese text, and more.
Chinese Converter: this website has several tools. It includes online Chinese input methods, a converter for simplified to traditional characters and vice versa, a tool that reads text aloud, a way to convert Chinese characters to Pinyin, and others. But be aware that the results on this website are not 100% accurate.