I periodically find myself amazed by concerts. The last one that comes to mind was by a polish band named Pink Freud. I went to see them just for the name and was completely blown away: tink of a mixture of punk rock energy, jazz freedom and inventiveness and King Crimson like precision.
Also Peter Hammill on a good night is fantastic, sadly he's not always on a good night.
The number of artists I wish I'd seen is countless, including some I wish I'd seen when they were good (I saw Genesis on the Calling All Stations tour, enough said), but I guess if I could timetravel just once to see a concert I probably would go back to hear Bach.
Nice post........thanks for replying ! Pink Freud sounds very interesting too !