Another one that has a profound effect for me is to tell the kernel not to probe unnecessary devices.
I’m working on laptop with a hard drive and a DVD-CDRW — assigned to ide0 and ide1, respectively, which I can see during a normal boot sequence.
I’m going to assume this machine prods no farther than ide2 and ide3 for the secondary master and slave device, and add these lines to my kernel boot line in Grub.
With this, my 300Mhz laptop gets to the login prompt in under 30 seconds. Adding X will no doubt make the boot time a little longer, but I think I have it down quite a bit over my best boot times now.