The ideal dictionary would be the one that basically combines both approaches and is twice as thick (or alternatively has half as many entries). UPDATE 1: It should not be just a regular dictionary with a frequency index.
Are there any? If there are, for what languages?
UPDATE 2: If you know such dictionaries, how good are they compared to regular dictionaries? Do they give good examples of word usage or are very stingy on this one? Up to date?
I'm just thinking that that would be the kind of dictionary I'd use more often because I'd be able to not only look up words in it but also read it going from the most frequent words to the least and improve the vocab in a more directed way, without leaving glaring gaps in case the stuff I read isn't very diverse in terms of vocab.