for on-ear phones that are easy to drive, my 0.02 would be to recommend the grado sr-225. these are "mid-priced" at about 200.00. they're fairly light, and the older models (before the "i" designation) means the cable is thinner and lighter. the newer 225-i models have the thicker cable which would probably make them a bit more cumbersome if you'll be using these mainly through a smaller, portable device.
but my take is that the 225's actually sound better through a laptop than the more expensive rs1-i's from grado that i have. the 225's seem to have more low-end out of the laptop than the rs1-i.
the rs1-i has just as much bass response as the 225, but the rs1-i has more extension up top and reproduces more high-end frequencies (which you may not want coming out of a portable device). horses for courses.
i think you'd get better results out of a laptop or ipad with the 225, rather than the grado 125 model, but here again, i've never heard the grado 325. these may be even better, though they'll be more expensive than the 225.
to me, i think the 225 occupies a real "sweet spot" considering price/performance for this category. but, here again seek out the older (but still new in the box version) that has the thinner cable.
just my take.
