The Boeing 777 has got so called 'raked wingtips' where the wingtips have a larger angle angle of sweep then the rest of the wing. This increases wing span and thus aspect ratio. According to tests from Boeing and NASA this gives a bigger drag reduction compared to winglets. On the other hand an increase in wingspan can result in ground handling difficulties, that's why on the most medium-haul aircraft winglets are installed.
Correct me if I'm wrong.