What firmware updates should I be tracking?

While Moab's thoughts can sometimes be correct you might not know it is an issue until it is broken or someone else takes advantage of your older firmware. Sometimes running new firmwares can get you but the same goes for running older ones and you can't trust the changelogs, they might resolve something they didn't want you knowing about.

Here is what I can come up with: home phones, cell phones, printers, network switches and routers, UPS, CD-Roms, DVR's

Adding to the list:
video card BIOS/UEFI updates
TV cards
I've heard of firmware updates for HDDs and SSDs.
keyboards (fancy ones to be honest)
fax modems (hardware fancy ones)
calculators (usually graphing ones)
Intel's processors (these usually go over Windows Update or BIOS update, because processor's microcode can't be flashed so it needs to be updated at every system start.)

Can't think of anything else at the moment.