This tip is in the ArchLinux Beginners Guide, but I have thought it was a good idea to repost it here, as it is a very useful tip, when you are using ArchLinux.
When you first install ArchLinux you will have a file /etc/pacman.d/mirrorlist where are listed a lot of mirror servers for all the world's regions, and it will try to use the very first one, and then if it fails the second, and so on, so maybe the first one, or the next are not the fastest mirrors for you, in order to have listed the fastest in good order do this:
First install python, as is a python script that will helps us to solve this.
sudo pacman -S python
Then go to where mirrorlist file is:
create a security copy of your mirrorlist file, do it as root
cp mirrorlist mirrorlist.bak
and run the script as root
rankmirrors -n 6 mirrorlist.bak > mirrorlist
You may want to have more than six, so -n [m], where m is the number of mirrors you want in your mirrorlist file.
Now, update the pacman's database
sudo pacman -Syy
This helped me a lot.