I don't like posters. After 4 years of living in a dorm, I had so many issues with sticking posters onto my walls. I went from sticky-tack which ruined the backs to plain old tape which tore into the print. I have partially ruined my limited edition Homestuck print (signed by Andrew Hussie) and tore through my poor Skyrim map.
Why not order a wall scroll instead?
I happened to come across this site:
Customwallscrolls.com which offered to print any image of yours into a fabric scroll. I have two scrolls myself: a Revolutionary Girl Utena one and a xxxholic one, both I got from Megacon 2011. I have had no issues putting scrolls up on walls. Just get some of those command hooks and--BAM--the scroll is attached to the wall fairly well.
A week or so ago, I ordered a custom scroll of one of my favorite anime/game characters: Nepgear from the Hyperdimension Neptunia series. I found a large image of her online, about 2000x2000 pixels, and sent it to them.