Quake1 Style Teleports:

I hate those teleporters in Q2, 'orrible sparklies etc :)

First, make a brush the size and shape that you would like your slipgate (also the texture you would like)
Now make it a func_wall entity, give it a spawnflag of 7 (trigger spawn, start on, togglable) or another as long as it has trigger spawn applied.

This will make it so your slipgate starts turned on, if you leave out the start on flag then the slipgate will only become active when the func_wall is triggered (have to give it a name though first :P)

Then, give your slipgate a target of an info_not_null - this will be the destination, and there you go, a 'slipgate'

NOTE: If you do not specify a target, it will act like a normal func_wall
NOTE 2: You only transport when the func_wall is active (you can see something)
NOTE 3: ALL teleports (the standard ones) no longer give off that little sparkly shower.

See the demo map for more info.