Pleco: this is the most comprehensive Chinese-English dictionary for language learners, available for download on Android and iOS. It can be set to simplified or traditional characters, and it also includes an optional Cantonese dictionary.
MDBG: a dictionary similar to Pleco that is available on web browser. Simplified and traditional characters
YellowBridge dictionary: This is another great online dictionary for learners. It shows you example sentences, similar words, and stroke order. Simplified and traditional characters.
iCiba (金山词霸): Free online dictionary from China. It provides translation into English, as well as a translation service, example sentences, and similar words. Simplified characters.
Moedict（萌典）: free and open-source dictionary based in Taiwan. The dictionary provides definitions of words in Chinese with examples, also including translations into English, French, and German. It also has sections dedicated for Taiwanese Hokkien and Hakka, as well as sections for Chinese proverbs and idioms (成語、諺語、歇後語、etc). Traditional characters.
Ichacha (查查造句词典): this is a website that gives you example sentences for any word or phrase, it's really helpful to understand the usage of new vocabulary. It also provides translation services for English and other languages, but the example sentence feature is the most useful. It’s available in simplified or traditional characters.
Leiden Weibo Corpus: This corpus comprises of over five million messages posted on Weibo, the most popular microblogging platform in China. By searching words and phrases on this corpus, you can see examples of how they are used online. Simplified characters.
Forvo: This website allows you to look up words to hear pronunciation from native speakers, which can be chosen based on region, dialect, and gender. It can be used for any language.
Zi.tools: this is another dictionary that provides information about Chinese characters, including pronunciation in several languages (Mandarin, Cantonese, Japanese, Korean, Vietnamese, etc.), historical forms, related characters, and more. It's an interesting resource, but for the average Chinese learners it provides way too much information than what is needed. The interface is in traditional characters but works for traditional and simplified.
Book and e-book dictionaries
Feel free to browse all the available dictionaries at the library in this LC subjects: