The Sennheiser HD598 is an open can. Also, it has a very different sound signature - way less treble and way more bass. Frequency graphs over at headroom back this up. The HD598 might not have as much of the Sennheiser veil as some of their other cans, but it still does have the famous Sennheiser house sound.
The DT770 is a good suggestion though, since it does have a Grado-like emphasis on the treble with a big focus on clarity. It does however also have waaay more bass than the typical Grado sound, but then again, nearly every can out there has more bass than a Grado