I really wish I'd kept a list of every one as it'd be really fascinating to chart my musical education !
First thing I saw was probably Elton John along with The Beach Boys, Chaka Khan,Beach Boys and others at Wembley Stadium - taken by my cousin probably back in 1975...
then,in no particular order ...
Loudon Wainwright 111 at Cambridge Folk Festival, Cheap Trick, The Tourists, The Clash (several times),Toots and the Maytals, Pablo Black, Magazine, Throbbing Gristle, The Slits,The Raincoats, Spizz Energi (or one of the variants), Bow Wow Wow, Crowded House, Jane Siberry, Pete Townshend, Aswad,The Rezillos,the Undertones, Laurie Anderson, Stereolab,Lemon Jelly.......and my mind has gone blank...some were truly fab experiences !