CRTs for definate - it's an inherant part of the design. If it didn't produce heat it wouldn't work.
Quick physics rundown:
Any CRT has, at the back of the tube, 3 wire coils (red, green, blue). These coils are heated by electricity passing though them to a couple of hundred degrees. This has the side effect of "boiling" electrons off the wire - they get so energetic they detatch from the coil.
Under normal circumstances, they'd just zip about randomly til they hit something and got canceled or joined. In a CRT, there is a sequence of electromagnets that first makes sure the electrons are moving towards the front of the monitor, and then focuses them to a point. Further electromagnets direct the beam across the monitor. The action of the beam hitting the screen produces the light output from the monitor.
So, basicly, a CRT is an electric heater with lots of electromagnets round it. Both electric heaters and electromagnets use large ammounts of power, and both tend to get rather hot.
LCDs, on the other hand, use pigmented red, green, and blue cells that can be switched from being totally opaque through varying degrees of semi-transparency by presence or abcense of a small electric current. The light output from an LCD comes from a flourescent tube light (or several) behind the cell panel, which shines through the semi-transparent cells.
This is a low power solution, so produces significantly less heat. No power hungry magnets or heaters here. However, the panels operate at low voltage, so a transformer is needed. This does produce heat. Often they are provided as a "brick" seperate from the monitor, so the total heat form the panel depends on where the power is transformed.
This concludes today's physics lesson.