I was thinking about this earlier, so I'ma do this for personal reference - I'm including live acts and DJ sets too:
Hounds
Doorly x2
Zane Lowe x3
Chase & Status x2 (One DJ set, one live set with added Plan B!)
Pendulum
The Prodigy
Nas
Damian Marley
Spragga Benz
DJ Semtex
Murkage
Yelawolf
Wu-Tang Clan
DOOM x2
Logistics
London Elektricity
Beardyman x2
Boys Noize x2
Sub Focus x3
Toddla T
Erol Alkan x2
Brodinski
Djedtronic
Strip Steve
Housemeister
Knife Party x2
True Tiger x3
DJ Hype
Friction
Dot Rotten
Donae'o
High Contrast
Shy FX x3
Netsky
Wilkinson
The Prototypes
Fred V & Grafix
Nero
Annie Mac
Outlandish
Andy C x2
Brookes Brothers
Caspa
Redlight
Deadmau5
Magnetic Man
Skream
Artwork
Labrinth (lol)
Kelly Rowland (lol)
Solange Knowles (lol)
Atomic Kitten (lol)
Professor Green (lol)
Rizzle Kicks (not lol - girls literally clawing on our backs to try get nearer the front ffs)
Breakage
Loadstar x2
Rusko
Totally Enormous Extinct Dinosaurs x2
James Blake
Vondelpark
Disclosure
SBTRKT
TONSTARTSSBANDHT
Grimes
Pantha Du Prince
and today I saw:
Raikes Parade
Paper Tiger
AND AMON TOBIN'S ISAM SHOW. IT WAS THE BEST THING EVER, FO REALZZZZ
Seen that people have seen Fleet Foxes, Bonobo, Rage Against the Machine, System of a Down... I'm seriously jealous.
I've not really been to any festivals - I went to one day of Parklife 2011.
From today I have lined up:
Shabazz Palaces
Belleruche
Parklife 2012
Jack White
Radio 1's Hackney Weekend
Bestival 2012
So expect the list to expand and become a bit more varied & representative of my taste. You might be able to tell I'm really fricken excited!