I have had the pleasure to attend every coachella and i have to say that from 1999 to 2011 there have been some big moments that only coachella can bring. From st. germains sunset set in 2001 to last years arcade fire's led ball dropping moment. Here are my Top 5.

1) the pyramid revelation Daft Punk 2006 (amazing and if you weren't there then you just don't know)
2) the bass on the Gloaming Radiohead 2004 (can be 2012 be better? i'll find out in less then 3 months)
3) coachella grounds erupting Rage Against The Machine 2007 (reunited and it feels so good)
4) guitar being played by pliers Portishead 2008 (yes they sounded better then prince and better then dark side of the moon that year)
5) 3 way tie here. sorry folks. Bauhaus 2005 (peter murphy hanging upside down like a bat and singing all of Bela Lugosi's Dead)
hearing most of 10,000 days Tool 2006 (they sounded real real good that night)
thom yorke and flea playing together atoms for peace 2010 (they did all of the eraser)

what are yours?