Do spells like Create Pit, Glitterdust, and Web break invisibility?

What about casting darkness on an enemies weapon?

What about casting darkness on yourself?

Any spell targeting a foe breaks it. If an enemy is included in the effect of Glitterdust, Web and Create Pit, then it's broken. If not then it isn't. Casting darkness on yourself wouldn't break it (but the darkness would be visible). Not sure about an enemy's weapon. I would probably conclude that targeting a weapon is like targeting a foe and rule that it breaks invisibility.

Yes.

Of course, the subject is not magically silenced, and certain other conditions can render the recipient detectable (such as swimming in water or stepping in a puddle). If a check is required, a stationary invisible creature has a +40 bonus on its Stealth checks. This bonus is reduced to +20 if the creature is moving. The spell ends if the subject attacks any creature. For purposes of this spell, an attack includes any spell targeting a foe or whose area or effect includes a foe. Exactly who is a foe depends on the invisible character's perceptions. Actions directed at unattended objects do not break the spell. Causing harm indirectly is not an attack. Thus, an invisible being can open doors, talk, eat, climb stairs, summon monsters and have them attack, cut the ropes holding a rope bridge while enemies are on the bridge, remotely trigger traps, open a portcullis to release attack dogs, and so forth. If the subject attacks directly, however, it immediately becomes visible along with all its gear. Spells such as bless that specifically affect allies but not foes are not attacks for this purpose, even when they include foes in their area.

So, all of the spells you've listed would break invisibility, so long as an enemy is in the spell. In the case of Create Pit, it wouldn't break invisibility if you cast it in front of the enemy, so it wouldn't affect the enemy. And if you were to cast Darkness on yourself, far away enough that the darkness effect didn't over lap the enemy, you'd be fine. But casting Darkness on the weapon an enemy is holding would break it, as the enemy is within the effect of the spell.