Shabbos and Yuntiff food warming is a problem which has long been solved...mostly.  Here are a few suggestions if you are in the market for a new one or want to improve what you already have.

Most American consumer models simply don't get hot enough.  The Israheat plata pictured above is nice and big and gets plenty hot.  So hot, it will heat the whole room and defeat your air conditioning.  You can moderate it somewhat by putting it on a timer like the GE digital timer and confine the heat to those times when you actually need it.

The plata is rated at 600 watts so if you don't want to blow everything else on the circuit, plug it into an existing dedicated applicance circuit like the washing machine on which it fits nicely.  If you buy or have another timer, make sure it's rated for at least 600 watts or it will fry.  The one above is rated for 1000 watts and has two outlets.

The timer instructions are skimpy and confusing, so practice before you need it to make sure your settings do what you think they'll do.  It allows 20 on+off settings.  There are 4 mode settings: on, off, auto-on, auto-off.  Do not be confused!  "On" means whatever is plugged in is always on; "off" means whatever is plugged in is always off.  To invoke the timer at a time when the device that's plugged in is supposed to be off, select "auto-off."  Plugging in the timer when the device is supposed to be on, select "auto-on."  The timer has a built-in 7-day clock with an internal battery, which should continue to run as long as it's plugged in to recharge once in a while. 

Incidentally the plata itself is no design wonder.  We've had two, each of which has lasted about 5 years, then gone "poof" in a cloud of smoke and sparks when plugged in (there's no "on-off" switch so expect a nice spark at the outlet when unplugging the unit).  Postmortems revealed the internal wiring had the wrong kind of insulation, not meant to be subjected to prolonged high temperatures.  The insulation had baked hard, cracked, and finally fallen off...allowing the simple act of setting up and plugging in the unit to jiggle the wires sufficiently to cross, touch, and short-circuit.  If this kind of surprise disturbs you, best stick with an underpowered American unit with an "on-off" switch, temperature selector, and UL (Underwriter's laboratory) seal of approval.