Fizzmix, let me add to that before you buy the Grados:
A lot of folks here will tell you buy the Grados since their sound is aimed more towards rock/metal. I personally listen to Metallica (old stuff), Fear Factory, Danzig, Helloween (time of the oath), Iron Maiden (live after death), Linkin Park, misfits, etc. I have the Grado Sr60's and they sound nice, but the Sony Mdr7506's sound much cleaner and just kick ass. The Grado's and Sony's both work well with a portable unit (i use a Sony Minidisc player). Since you state you are willing to use a portable amp, then i can only suggest the (slightly large) Sony's. Also, the V6 model (NOT V600) is identical and can be purchased here:
http://shop.store.yahoo.com/hogwildstore/mdrv6.html
Thanks to Desben for the above link!!
Check out for the Grado's here:
www.headphone.com
Simple comparison between the two (in my opinion):
Grado's: decent bass and crystal clear highs, slightly muddled midrange. Cumbersome (very thick) cord, open cans so you hear everything around you (dont even bother using these on a train) and everyone can hear what your listening to. Use these at home most of the time. Overall i was/am very happy with these.
Sony's: Excellent highs and deep lumbering bass (not over powering). I have no arguments about the sound quality, they are superb for their price easily beating out the Grado's in my opinion. Also a lot of folks say these cans are analytical, which i must agree. If a recording sound bad, there just going to sound worse since these have a lot of detail in them (and if a recording sound great, its going to really shine on these cans). The only complaint i have is that the cord is coiled. Also, these are closed cans so they block out some sound to a degree. I use these outside everyday. I suggest these cans over the Grados.
As for a more expensive pair of headphones, lots of folks will probably say get the Grado Sr225's for your genre of music. I havent heard these myself, but i'm very curious to hear them. Check out
www.headphone.com for a list of grados.
I hope this helps a bit and i wish you the best of luck! Please post reviews of whichever cans you purchase.
George