Note: The difference between a normal divination spell and a divination spell of the scrying subschool is the divination spell’s creation of an effect that’s a magical scrying sensor, the presence of which can be noticed with a successful Perception skill check (DC 20 + spell level) and through which the caster can use its own senses. Thus if a spell does not have as its effect a magical sensor, the spell really shouldn’t be part of the scrying subschool. Of course, some spells are anyway.
There are currently under 20 spells of the scrying subschool

In the Pathfinder Roleplaying Game Core Rulebook only four spells are in the scrying subschool: the 3rd-level Sor/Wiz spell clairaudience/clairvoyance, the 4th-level Sor/Wiz spells arcane eye and scrying, and the 7th-level Sor/Wiz spell greater scrying, but the crystal ball and magic mirror are so iconic—and the scrying spell such an important weapon in a GM’s arsenal—that to devote extra attention in the core rules to the concept of peeping on folks when they likely don’t want to be peeped on isn’t unwarranted.

The list of later scrying spells that actually have as their effect the creation of a magical sensor includes the 3rd-level Sor/Wiz spell gilded whispers; the 3rd-level Sor/Wiz spell mirror sight; the 3rd-level Clr spell riversight; the 4th-level Clr spell traveling dream (noteworthy in that it creates a scrying sensor the size and shape of the caster’s body that’s automatically visible but only to animals and children); the 5th-level druid spell jungle mind (which uses a picked preexisting animal as the spell’s scrying sensor, which is a little weird); and the 5th-level Sor/Wiz spell symbol of scrying (the symbol—like the effect created by the spell symbol of death—apparently also being the sensor, but this could’ve been clearer).

Although they’re officially part of (enrolled in?) the scrying subschool, some spells that don’t have as an effect a magical sensor are tossed into the subschool, too. These include the following:

The 2nd-level Sor/Wiz spell track ship which creates as its effect a magical icon on a map that’s in the caster’s presence.
The 3rd-level Brd spell witness which creates no effect.
The 3rd-level Sor/Wiz spell spherescry which allows the caster to perceive through onyx spheres, yet the spell “produces no indication of its activity on the target [onyx spheres] and cannot be discovered by normal methods of magical detection.” The spell creates no effect.
The 4th-level Sor/Wiz spell share senses which creates no effect, simply allowing the caster to experience its familiar’s senses.
The 5th-level psychic spell remote viewing which creates no effect and really doesn’t follow any of the scrying subschool rules at all.

Precedent was set for there to be spells that acquire information at a distance yet not be of the scrying subschool in the D&D 3.5 core rules (on which Pathfinder is based) by spells like prying eyes et al. (also in Pathfinder) and discern location (also in Pathfinder), but Pathfinder seems to be gradually broadening the scrying subschool.

However, a Pathfinder-only spell that gets this exactly right is the 4th-level Sor/Wiz spell questing stone which is a divination spell based on the spell arcane eye but that uses as its sensor an ioun stone, excluding questing stone from the scrying subschool.