I'm afraid I can't answer your remaining questions for you, but I will contribute what little I can to your quest.
I do a lot of reading here, mostly shopping for things I can't afford, and it's absolutely uncanny how every time someone makes a post considering the purchase of sub-100 dollar Grado, ten different people will jump in and advise that they instead go for Alessandro MS-1. Apparently the MS-1 is based on the supposedly higher-end Grado SR-125i, and not only that, but improves them, and can be got for 100 USD, which is a huge boon if you're outside of the US because Grado are expensive to get elsewhere. I can tell you that my experience with Grado SR-60i, my first and only pair of quasi-serious headphones, has been great (unamped). The bass sounds powerful to me, where after a year with the things I'm starting to get a little overwhelmed at the mids and highs. It's all just too much sometimes. They sound really detailed and big to my ears, but they're also the only decent headphones I've ever used.
That being said, I too am looking to buy some full-size headphones in the 100-150 range, possibly higher, "upgrading" from my SR-60i. It's essential that they sound great unamped, as I don't have the education to amp or whatever else you do to the signal. However, potential for upward growth should I ever come into that knowledge is a big plus. Sound isolation is not an object. I'm not looking at any Grado or the Alessandro for obvious reasons.
Commendations for phones on my list, recommendations for phones not on my list, personal experiences, physics lessons, and high-handed derision at my unseasoned naivete are all welcome!
Looking at
AKG K-240 (~100)
Audio Technica ATH-M50 (~100)
Audio Technica ATH-AD700 (on sale at amazon for $94.61)
Beyerdynamic DT 440 (~100)
Sennheiser HD448 (~100)
Sennheiser HD555 (on sale at amazon for $90.72)
Sennheiser HD595 (on sale at amazon for $139.99)
Shure SRH440 (~100)
Shure SRH840 (on sale at amazon for $149.00)
Sony MDR series
I Like
Rock: noise rock/noise pop, punk rock, shoegaze, post-punk, experimental rock, "rock and roll", folk rock (with reservations), college rock, jangle pop, non-insipid indie rock, art rock, post-rock, psychedelic rock
e.g. Nirvana, My Bloody Valentine, Sonic Youth, Pavement, The Velvet Underground, Sigur Ros, Bjork (for lack of a better category), Pixies, R.E.M., Radiohead, Sufjan Stevens, The Flaming Lips (The Soft Bulletin mostly), The Smiths, Talking Heads, Nine Inch Nails, Bob Dylan, Yo la Tengo
Hip Hop: East-Coast, West-Coast, Trip Hop, Gangsta Rap, "Alternative" hip hop, Acid rap, Conscious hip hop
e.g. Kanye West, Mos Def, Common, Gang Starr, Wu-Tang Clan, Ghostface Killah, Raekwon, Ol' Dirty person, DJ Shadow, Bjork (for lack of a better category), Cannibal Ox, Young Jeezy, Lil Wayne (almost exclusively Tha Carter III), The Notorious B.I.G., 2Pac, some Jay-Z, Big Pun, Immortal Technique, Eric B. and Rakim, Gucci Mane (his talent, not his music), and of course M.I.A.
Other: I know nothing about Jazz but I would like to learn. I listen to about as much classical as the next guy/girl. Some House. Some IDM (intelligent dance music). I hate that term, but you know the kind of music I'm talking about. Pop that actually works (Madonna and her ilk). Aphex Twin is good.
I Just Can't Do
Any metal, prog *genre*, techno, Baroque Pop, Coldplay, King Crimson, Music for People Who Go to Conventions, Music for Linux Users Who Actually Only Know a Little Java and Some Scripts, Music to Read Webcomics by, etc.