If you don't want isolation and don't mind carrying an amp around, the Stax SR-001 is the best sound you're going to get. In a library ambient noise isn't an issue, and noise leakage from the 001 is minimal, so you'll be fine to go. I used it at the library in my college, and even though I couldn't get any studying done with the things in my ears
I definitely loved the sound. Rich, warm, lush, inviting, and ultra-detailed. These things are so fast it's ridiculous, and their ability to resolve complex passages is second to none. The treble is a bit rolled-off, at least next to the Grados, but that just makes them less fatiguing.
If you do want the isolation, though, then the UM2 is probably a good bet. It's smooth but forward - like a smoother version of your grados. Not as good IMO, but not a major step down in quality either.