Astérix, from French to UK English (they did some specific US translations awhile ago, but those were boring and sucked).
The Astérix albums are very pun and cultural reference-heavy, and translators Anthea Bell and Derek Hockridge did a brilliant job finding British equivalents that were often just as funny and fitting, if not more so.
For more "literary" works, I'd have to say various translations from the
Oulipo movement, simply because of sheer technical difficulty on top of the usual one-language-to-another issues.
Especially
that book which was written without using the letter E, which the translators have apparently taken it upon themselves to try and replicate said feat in their own languages. One day I shall have to try collecting their efforts, whether or not I can actually read them.
As for Oulipo translations I've actually read and can compare to the originals, I myself own two different illustrated versions of
Exercices de Style, and have read both the very nicely adapted English translation, and also the excellent graphic novel homage, from the library.