I’ve uploaded a PKGBUILD for ibus-unikey to the ArchLinux AUR. You can install it with yaourt like this:

yaourt -S ibus-unikey

If you don’t want to build from the source, you have to install all the dependencies first:

pacman -Sy gcc gconf gtk2

And then download and install the binary package

Then add the following to your .bash_profile

export XMODIFIERS=@im=ibus
export GTK_IM_MODULE=ibus
export QT_IM_MODULE=ibus

PS: Ok, there is no spyware/malware/rootkit in this binary package! If you don’t trust me, don’t use this method and build the package yourself (this is the way I recommend)