1. Angled Earpads - the AKG x7xx headphones, also the LCD-2 (and later versions) and the VTX version of the HM5, all come with earpads that are thicker towards the rear (behind the earlobes). While the driver mounts themselves aren't angled, these effectively angle the drivers relative to the ears. As for actual angled driver mounts, off the bat, there's the Beyerdynamic T1, Sennheiser HD800, and the Sony that looks like it inspired the HD800. For extreme angles, there's the AKG K1000.
2. The real problem: driver position relative to the ears. The real problem with headphones vs speakers, aside from each ear not hearing the driver on the other side, is the direct path of the driver into the ear canals - if you set up speakers to the same angle directly to your left and right the treble will be harsher and the imaging will also be problematic. Angled mounts don't just mimic the toe-in on speakers, but also avoid this problem by not having the driver directly firing into the ear canal. With headphones that do not have angled mounts or earpads, this effect can be replicated by wearing them in such a way that you avoid having the drivers directly over the ear canals by wearing them slightly forward of what conventional wisdom tends to dictate. With Grados for example instead of having the rear sides of the earpads slightly past the earlobes, move them forward so the rear sides fall short of the earlobes.
My own procedure with the HD600 is to put them on "normally," then push them forward so the earlobes rest on the rear side of the earpads, somewhat folded forward (not to the point of discomfort). This is enough to significantly reduce the harsh treble as well as sufficiently correct (on the Sennheisers, but less so with the Grados; although they have less of it to begin with) the trident-shaped soundstage of conventional headphone listening, with a strong L-C-R and recessed imaging between L-C and C-R. You can try this now for free with any headphone that you currently have.
