I have tons of GD & Garcia concerts. Some are even done in 24 bit/96 khz. And you can hear the difference.
I put my system together by how it made the Grateful Dead and a whole bunch of classical and baroque music sound.
I listen through a meier stagedac, Lehmann audio Black Cube Linear and HD800s. When I listen to some of the old concerts it reminds me of what it sounded like when I was there, no mean feat, For example, some of the early 80s shows from the frost or berkley sound pretty close to how I remember the show sounding when I stood near the front. Likewaise I have some garcia/saunders from The Keystone in '73 in 24/96 that recalls a sound that I hadn't heard in many, many years. I think its from the same run of shows that they made the album from. It sounds much better than the album.
Does this setup reveal flaws in the sources? of course. But also reveals all kinds of little things in the interplay between the jerry and the boys that I didn't here in other setups, while sounding like I think the band ought to sound. And nowadays you can get amazing sources off etree and other places and in some cases the sound rivals or betters some of the official releases.
This is a long winded way of saying that unlike the poster above I would get the best equipment you can afford. Personally, I don't like the grado sound. Many people think it is the ultimate in Rock & Roll, but I find it oddly colors the music. And I don't think Garcia's guitar sounds like i remember it sounding through Grados. You'll have to try it out for yourself. I do like the senn hd650 as well and it is more forgiving than the HD800 of source flaws.
I used to see phish quite a bit when they were still playing clubs, but kinda stopped seeing them after they hit it big. Anway, near as I can tell what i said about the dead applies to phish too.
For just the ipod or laptop situation, I think you could go with the senns listed above, quite nicely and that is a good start. For a bit more money, you might look into the Beyerdynamic t50p that is about to be released. I have to offer a big caveat: I haven't heard them yet. They are based on the same technology that their flagship T1 cans are based on, designed for portable, no amp use (although an amp will make them better). The the T1 was the closest I have heard to my precious HD800s and some Headfiers prefer the T1, I don't but I can see why they do. So I expect the t50p will be great for no amp situations. If you wait 3-4 weeks you will be able to hear what early adoptors at head-fi are saying.
If you want to spend a bit more, there are many inexpensive and ok sounding budget DAC amps. The poster above recommended the FUN which is probably a great choice, I own its predecessor the compass and think it was great for the dough spent. But there are some less expensive ones that are ok too. You can search the forums.
Enjoy the tunes and the long strange trip through head-fi.!