I was looking at Coachella's lineup for this year, and while it looks really good, I went in 2004 and I have to say that was one of the best line-ups I've personally ever experienced.
2004 Big Acts (that I enjoy/ed)
Pixies (Reunited)
Radiohead
Wilco
Rapture
Trail of Dead
Phantom Planet
LCD Soundsystem
Flaming Lips
Air
Belle & Sebastian
Bright Eyes
Mogwai
Muse
BSS
PGMG
That got me thinking, what would your ultimate lineup be? It wouldn't have to be as many as Coachella obviously, which attempts to cater to a broad and diverse audience...the downside of which is that while you see one band you really enjoy, chances are you're missing out on another band you would also enjoy. You could set up your list so that the artist plays right after another. Feel free to throw in bands that would "reunite" for your festival! But try to keep it reasonable!
However, personally, I would refrain from raising the dead.
That being said, my line up would be like this (play right after another, first band listed is first band playing). 20 bands, two days. Mostly just bands I'm really digging right now and would love to see all together.
Day 1
Voxtrot
Destroyer
Band of Horses
The Panda Band
Stars
Interpol
Cat Power
Teenage Fanclub
Wilco
TELEVISION
Day 2
The Softlightes
Architecture in Helsinki
M. Ward
Broken Social Scene
Belle & Sebastian
Rilo Kiley
Wolf Parade
My Bloody Valentine (Reunited)
The Flaming Lips
PINK FLOYD (Reunited, no Syd Barrett though :[)