Well, if a ship has chemical rocket engines, it can explode pretty conventionally after being hit. A fission rocket engine could explode if it was somehow able to get clogged. Some sort of fusion drive I don't know about, since nobody's designed one yet.

Weaponized lasers would most likely not be emitting visible light at all, but would more likely be either longer-wavelength (infrared or microwave), or maybe higher (I'm not sure about ultraviolet lasers, but an X-ray laser would be a pretty fearsome weapon, if you could build one.)

A powerful laser firing in air can very well be visible, though, because it ionizes the air it passes through. In space, you wouldn't have that, but debris from the battle might work the same. Actually, I wonder if some sort of cloud of small droplets or particles wouldn't be a good counter-measure against laser weapons...

If you are having a battle in low orbit with nuclear weapons, though, I wonder if it wouldn't look sort of spectacular from the ground, if the weapons are powerful enough to start affecting the ionosphere. High-altitude nuke tests have caused some quite spectacular effects. See the Starfish Prime test here: http://nuclearweaponarchive.org/Usa/Tests/Dominic.html. Of interest is also the Argus tests: http://nuclearweaponarchive.org/Usa/Tests/Argus.html.

(I love this thread.)