While idling in #archlinux on freenode, I came across this neat little trick to speed up downloads in pacman.

First install the package axel:

pacman -Sy axel

Then, edit /etc/pacman.conf:

XferCommand = /usr/bin/axel –output=%o %u

The next time you update/download a new package, Pacman will now use axel to download the necessary files.  Axel will try and make multiple connections thereby taking less time overall to download.