This is the official review of Halo 3 "Wall Graffix"(one of the several designs) for your wall, this design here was created by Gamer Graffix.
MSRP 19.99, you can buy it from there website or at Target (most likely other stores as well, but I have seen them there)
+ The price is just about right
+ Very cool looking
+ Reusable, you can move it around
- If you don't clean your wall first it will fall off
- I wish there were some more designs