Electric floor!
I have thought of making some kind of electric floor or something (exactly what is not important, the point is: we can't go there inanimate objects can!). using a trigger_hurt or something will do this nicely, but the problem is having a fitting effect/sprite/particle system.
Is there any nice, fitting effecs floating around, and if that's the case, how do I actually create the effect?
You could try placing a few small env_sparks, and maybe some sparking wires under broken floor tiles if it's not supposed to 'intentionally' be broken. I don't really know of any particle_system effects...
A few sparks would help yes, but my floor is an intentional part of a puzzle chamber, so I hoped for some arks or a particle field like the fizzlers or something. 
There aren't any official ones that I know of, you could look through some of the sprites and have a few env_sprites as well as a few sparks
My real piece of advice here is make a custom texture for the floor which is clearly different from normal floors but also clearly recognisable as a portal style floor - so perhaps keep it tiles of the same size or something.
Also make one of those indicator signs with a man getting fried
What was the shiny green field used by espen180 in post-portal? It's better than nothing?
Hi!
I've made a kind of similar concept on my experiments map involving electrified water.
Basically, the visual effect involves:
-Water
-A blinking blue light
-Tesla lighting arcs point_tesla to make the lightening effect
-Sound loop activated when the water is electrified
Water makes the dangerousness of the section belivable, as everyone knows that water and electric arcs means no good. So it's an easy way to say that you should be careful, as a simple texture would require further explanation.
The main problem is that the tesla arcs and the light need a logical source. In my case I used a ball catcher placed underwater and initially active.
Author of Minecraft mods (MAtmos, Minaptics, NoteSlider) and Garry's Mod addons (Gunstrumental, SharpeYe, GarryWare, DepthHUD).
I've made a kind of similar concept on my experiments map involving electrified water.
Basically, the visual effect involves:
-Water
-A blinking blue light
-Tesla lighting arcs point_tesla to make the lightening effect
-Sound loop activated when the water is electrified
Water makes the dangerousness of the section belivable, as everyone knows that water and electric arcs means no good. So it's an easy way to say that you should be careful, as a simple texture would require further explanation.
Know! Your electric water is really sweet ^^
It was kind of my backup plan 
Edit: Is it possible to make the arks move horizontally only? Placing the tesla at the middle of the floor and the arks spreading throughout the whole floor would be sweet!