"Money, so they say
Is the root of all evil today
But if you ask for a raise it's no surprise that they're
Giving none away, away, away"
- Pink Floyd
Enough nostalgia, back to the question:
Frequency dictionaries tend to cost about $35 to $45 (US).
The Wikipedia frequency lists are also fine, and they have a pretty attractive $0 price tag.
Barron's publishes books that sort words by topics, which is handy. But eventually, you may want to just make sure you have cards for the most frequently used words-- the top 1000 words, then 2000, then 3000, etc.
The Routledge list for Japanese is awesome once you finish the 625 words list. It has excellent translated example sentences that show you exactly what the word means. Save time by using those example sentences immediately in Anki to learn the words. They also provide parts of speech, gender, and proofread translation. In the Japanese list, they group together alternate spellings for single words (which would be two separate entries on the Wikipedia list). These features make the cost worth it because they save you time in the long run.
