I've tried to install new arch linux today, failed however. There are a lot of packages missing like fdisk or gdisk, there is no dhclient which made it difficult to connect to the network and for the most curious thing - there is no pacman. How am I supposed to install any package after initial media boot? I remember these packages were present on older releases, is there a new way to install the system or something? The image I use is archlinux-2015.09.01-dual.
As it turns out the image checksum was correct only the media was prepared incorecctly. Everything seemed to work besides those missing packages. I've made that pendrive using rufus on windows and choose the iso mode, that was causing the trouble.
So basically if you wish to use rufus tool select the DD mode and it will write the image correctly.