Nice topic! :D
I saw Jethro Tull in Bristol last year, they were touring with a classical violinist named Lucia Micarelli, and performed some quite amazing tracks together as well as all the Tull classics.
It was not at all what I was expecting, which was a bunch of creaky old rockers looking very creaky and sounding a bit creaky with me overdubbing thier creakyness with a nostalgia track in my head.
Instead they blasted out a good 2.5 hours worth of new and old material, all delivered with the energy and amazing musicianship they have always been famous for, and Ian Anderson is one funny guy! He told jokes and interesting little stories all night.
It was more like 'an audience with Jethro Tull and friends' than a straight-up music concert. Truly great stuff.
As amazing as JT were, I'd have to say my favourite Nostalgia moments were seeing a band called The Musical Box doing their Gabriel-era Genesis tribute shows a few years ago.
I saw the Selling England, Suppers Ready and Lamb Lies Down tours and they were jaw-droppingly good. The tours were made to be as close as possible to the actual tours that Genesis did, and they went as far as talking to the guys from Genesis and getting tips on set and prop construction, and even borrowing costumes and instruments from them.
Some of the tracks I could honestly not have been able to tell if the record was playing or the band were performing, they were that good.