The Grado is the most different sounding headphone with VERY forward mids and treble - for some genres this just comes off as grating, harsh and just annoying - but for pretty much all rock/metal it just brings out guitar riffs to toneful, aggressive perfection. It sounds very much like you'd expect a live amped guitar to sound.
It's an acquired taste, so if you're looking for variety (which is fine by me) but don't have a DAC and amp you should do your wallet a favour and have a look at the SR80i - without a half decent source you won't hear much difference between the two.
ATH M50 is a pretty good all-rounder headphone. It does a lot of things very well, but nothing perfectly - but should have a better bass presentation and slam for energetic hip-hop than your current headphone line-up.
Also doubles up as a pretty good outdoor/portable headphone.
But if you're open to suggestions for home-use only, a professionally modified Fostex T50RP MKII will do both rock and hip/hop and almost everything else nearly perfectly - the only catch is you'll need to get at least a basic amplifier and DAC for the investment worth the while.