I have a ton of guitar emulators - Pandora, Zoom, Pod, Pod Xt, software (Logic), even the original Rockman. Sony MDR-V6 works great (not V600, those are awful).
One thing to watch out for - if you play rock or distorted tones, you may eventually blow pretty much any headphone you plug in - the MDR-V6 are the most sturdy (I've had pairs for years and never blown them), but I've blown out other pairs. I wouldn't plug in anything too expensive, since you might fry them (a guitar amp/tone emulator, especially with any rock tones, puts out some wicked transients and can kick your poor headphone's drivers or voice coil to oblivion).
The Sonys are a great choice for playing guitar because they are bulletproof, very efficient (so any headphone jack from a little guitar rig can drive them), not too expensive (typically $79 or so if you find a good deal), and sound very smooth and nice with guitar. They are not fatiguing, too, which is great when your doing long practice or jam sessions.
Note the MDR-V6 cans are not super accurate, so if you are recording with other instruments make sure to monitor with speakers (and/or other, more accurate, headphones). The Sony's will not let you know when you have too much bass bloat, and don't have the same super midrange detail you'll get from Grado/Allesandro. They (like most headphones) don't really tell you what's gonna happen when you listen to the music through speakers, so always monitor with speakers if recording. Most of their flaws in this area are with drums and more complex layered instruments, which is not usually an issue when practicing guitar or playing solo guitar.
BTW - in this context (playing guitar) I use them for everything from swing jazz to blues (with clean tone) to crunch blues to heavy metal.
-- Gordie
