I will second the Audio-Technica ATH-A900/AD900. I own the A900 and they sound great, and are sealed. Have great soundstaging despite being sealed. The only complaint people may have is the recessed mids, which in my opinion are not as recessed as some people make it out to be. They can do everything pretty well, and in my opinion would pull off rap the best out of all of your options.
Beyerdynamic DT770s I hear have wonderful bass
, and are also sealed! Never used them, but I hear them recommended often.
HD555 are a great choice, but you may also want to check out the HD595 as well. I haven't A-B'd them, but the HD595 sound great, but cost about $70 or so more than the HD555. Whether the audio upgrade is worth that extra cost I cannot say. Great for classical music, and can do indie rock pretty well, though not my personal preference, but that is a matter of preference and does change from song to song. Also, with indie rock (???), there is such a variety of music that falls under that label, it's hard to say.
The Grados are great, especially for rock, electronic, and in general indie music. They are not that great for classical, but can pass. They have wonderful detail, and are very fun headphones to have. But they have comfort issues with some and lack the soundstaging the Sennheisers and Audio-Technicas do.
I hope this helps, and take everything I say with a grain of salt. I am merely a novice compared to most on this forum. I own a Grado SR60, and the ATH-A900, and I've used my friends HD595 several times. So I feel I can give you a honest assessment of these. Most of the grados have a similar sound signature, just you get more refined headphones with slightly different balances.
If you were to list what music you listen to more specifically (delve more into this Indie music??), that would help.
