The resources listed here are very useful, somewhat useful, or minimally useful. A
short description after each describes its usefulness.
http://m.sanakirja.org - This
is likely the most useful online Finnish dictionary due to its thorough search results and
the visibility of the definitions amidst ads. Also, if you click the link labeled Pelit (English: Games),
you can access games for learning vocabulary. If you speak multiple languages, you can
enter a word in English or another language, and read definitions in many languages.
Note: To view a less cluttered and simplified interface, use the mobile version.
http://bab.la - This dictionary has a
useful auto-complete feature as you type in a term, but the search results are visually
cluttered by ads.
http://käännös.com - This
dictionary is useful as a cross-reference. It contains a lot of redundancy and noticeably
lags during search queries.