We use two different ones. Both are Brother products that have adjustable font sizes.
For faceplates we use a P-Touch (model PT-1800) with a 1/2" tape. We use a smaller font for this and make our labels similar to this:
WC1 PP1 P1 P2
where WC = wiring closet, PP = Patch panel and P = port number
Most of the time I cut the last port number off with scissors (or my side cutters) after trimming the ends and put the first portion over the appropriate port in the faceplate and P2 would then go directly over the second port. This label tells you at a glance, which wiring closet, which patch panel and which port on the PP the Keystone terminates to.
For labelling cables we use the Brother P-Touch Pro (model: PT-1650) with a 1" tape. Again, font size is adjustable. Rather than print lengthwise along this tape, we print down the tape.
ex:
RK-C2 P24 to
Net4sw01 P1
RK-C2 P24 to
Net4sw01 P1
RK-C2 P24 to
Net4sw01 P1
and wrap the tape around each end of the cable just above the RJ-45. (That's two labels per cable right)
RK = the rack number (we have multiple rows of racks in our data center with Cat6 running across overhead trays to PP's in every other rack in the rows) The rows of racks are numbered alphabetically so RK-C2 would be the second rack in the 3'd row etc etc.
P = port number in all cases
The label shows which port on which panel in which rack...which coincides exactly with the Patch Panel at the other end where our racks of switches and patch panels reside. The patch panels are labelled according to the rack they come from.
We include the switch name and port number the cable plugs into on that switch. This makes it a lot simpler to know where a cable goes should you (or someone else) unplug one for any reason and then not plug it back in.