You need the following libraries. The version given is to be understand as the minimum
version. However, if any of these libraries changes the API, i3 may not compile anymore.
In that case, please try using the versions mentioned below until a fix is provided.

 * xcb-proto-1.3 (2008-12-10)
 * libxcb-1.1.93 (2008-12-11)
 * xcb-util-0.3.3 (2009-01-31)
 * libev
 * flex and bison
 * asciidoc >= 8.3.0 for docs/hacking-howto
 * asciidoc, xmlto, docbook-xml for man/i3.man
 * Xlib, the one that comes with your X-Server
 * x11-utils for xmessage (only for displaying the welcome message, so this is
   mainly interesting for distributors)

Recommendations:
 * i3lock for locking your screen
 * dmenu for launching applications

Get the libraries from:
http://xcb.freedesktop.org/dist/xcb-proto-1.5.tar.bz2
http://xcb.freedesktop.org/dist/libxcb-1.1.93.tar.bz2
http://xcb.freedesktop.org/dist/xcb-util-0.3.5.tar.bz2
http://libev.schmorp.de/
http://flex.sourceforge.net/
http://www.gnu.org/software/bison/

http://i3.zekjur.net/i3lock/
http://tools.suckless.org/dmenu