The other day I was contemplating teleportation in D&D 3.X/Pathfinder, and began considering alternatives to the traditional form in which D&D teleportation came in. My favorite idea was one in which teleportation requires a caster at both ends opening two portals for safe travel. This also brings up interesting problems of whether or not to open a portal in the first place so as to potentially allow enemies to access your location instantly, or to necessitate interesting adventures in which the PC must negotiate with a distance mage to open a portal, or for the PCs to sneak into a location and open a portal for a large force to access (and I'm sure many other scenarios).
Of course, to make this relevant for more than a few levels, you may consider making other forms of teleportation should probably be removed from the game, or made harder or more dangerous to use than normal.
Casting Time 1 standard action
Target you and touched objects or other willing creatures
Duration concentration, up to 10 min./level (D)
Saving Throw none and Will negates (object); Spell Resistance no and yes (object)
This spell opens a portal and makes you aware of the direction and distance from your location of other open portals within 100 miles per caster level, as well as the alignment of the caster, if any, who opened the portal.
At any point during the spell's duration, you can attempt to instantly travel to any of the other open portals that you are aware of as a move action. Interplanar travel is not possible. You can bring along objects as long as their weight doesn't exceed your maximum load. You may also bring additional willing Medium or smaller creatures (carrying gear or objects up to its maximum load) within 30 feet. A Large creature counts as two Medium creatures, a Huge creature counts as four Medium creatures, and so forth. All transported creatures appear within the 30 feet of the caster of the target portal; if this is not possible, the action is wasted and no one is transported. As with all spells where the range is personal and the target is you, you need not make a saving throw, nor is spell resistance applicable to you. Only objects held or in use (attended) by another person receive saving throws and spell resistance. Traveling in this way instantly ends the duration of this spell.
When another creature attempts to use your portal, you become aware of its alignment and caster level (if any) and may attempt to bar it entry. This is resolved as an opposed caster level check.