If you start many services at boot, edit your /etc/conf.d/rc so that you have a line reading RC_PARALLEL_STARTUP="yes"
This will start up some services in paralel to save time at bootup.
On archlinux, you can let a daemon start in the background (which means parallel) by prefixing it with an @ in the DAEMONS array in rc.conf. For example mine:
DAEMONS=(syslog-ng acpid !pcmcia network @firestarter !netfs @alsa @crond @cpufreqd !laptop-mode gpm)
( ! is a quick way to disable a daemon without removing it from the list so you can easily enable it later)
I guess many arch users already know this since it is in the comments in rc.conf, but it's a somewhat new feature so if you set up your system before this was implemented AND never looked at rc.conf.pacnew, then you may not know about this.
and using a kernel without modules helps as well - hotplug is the most time consuming part of the boot, or at least it was when I last checked...
You could disable hotplug and load the modules using some script.
For some reason the initial loading of the kernel is very slow on my laptop, loading modules is much faster, so I made my kernel highly modular. YMMV.