To label electrical wires, bags for student activities, photography equipment, or Printed Circuit Boards (PCBs), I've used a few label printers. The use of a label printer is more efficient than labeling things by hand. If you run a lab or facilitate student activities, you can make things easier by obtaining a labeling machine.
There are a few products that I can recommend.
Dymo LabelWriter is cute, small, and connects to your computer. A large number of labels for addresses are available. I use this printer for mailing labels, student activity bags, and for labeling hard copies of photographs.
Dymo LetraTag is a small labeling machine that is good for your home and office. I've used this cute little machine for many years and I just love it. It runs on AA batteries. The labels are not as durable as the ones utilized by the Thermofox, but this machine works well to label drawers, cabinets in an office and folders. The writing on the labels can eventually decay under UV light, so if you need a more durable solution, please read on.
Phoenix Contact Thermofox is useful for creating labels for marking industrial equipment, PCBs, lab vials and drawers. It can be attached via USB to a computer. Consider purchasing the unit with a battery so you will not have to use AA batteries, or use the printer with an AC adapter. A word of caution: I've found that the printer can sometimes freeze up and refuse to operate, but this can be easily mitigated by removing the batteries and waiting for a few minutes before re-applying power.
For outdoor labels, a Brady BMP71 works very well. This printer has a high cost, but the labels created with this printer will not peel away from enclosures at a field site. The labels survive in warm and cold conditions.
I've also tried the BMP21-PLUS, but I've found that the cartridges can be difficult to obtain and for some strange reason I like the Thermofox better (perhaps due to the user interface). This is my choice of machine when travelling and I suspect that it is used by quite a few electricians and network hardware installers. I've used this machine for labeling PCBs and wires.