the best one that i have seen is a brady labelmaker. The printer itself can connect to a computer for all sorts of fancy label making, but in terms of suitability for electricians it is amazing. It prints wire numbers on inserts for sleeves and will serialize/increment them, on heat shrink tubes, and magnetic pushbutton labels are available.
On the spools for the material to be printed on, it also featurs an id chip of sorts that contains the details of how much printable room there is, etc which makes it easy to change spools without worrying about settings.
it came in a heavyduty case, with a mains charger/adaptor and is also battery powered.
http://www.bradyid.com/tls2200
