Save or fail spells 3 or lower

[Renen]

What spells do you gents know (level 3 or lower) that would be utterly devastating if you could make sure the enemy failed every save it made?

[HolyCouncilMagi]

Um... Grease is a nice start. An enemy that keeps trying and failing to stand is basically a non-factor.

[JDL]

Depends on your class. What do you want, Wizard, Cleric, Druid? Ranger, Paladin, Bard? Assassin? Blackguard? Expert?

[Renen]

Any spell but I guess sticking to wizard and cleric ones is fine.
With grease you could arguably crawl out though. Im looking for something that will either incapacitate the enemy, or render then unable to defend themselves as damage or CdG is landed on em.

[GunbladeKnight]

Sleep, Deep Slumber, and Entangle for sure. There's some good low-level Power Words (Power Word: Sicken), but I can't remember where they are in (I think Dragon Magic?). Hypnotism and its ilk are good, too. Daze is a single round, but a 0 level spell. Charm Person turns an enemy into a potential ally. Color Spray, Glitterdust, Blindness/Deafness are also good. And Hold Person and Slow are also good.

[Rubik]

Sanctum Spell'd Dominate Person.

The reason why is obvious.

"Oh, it's not really level three," you say?

It is if you scribe it as a scroll.

[Renen]

Well making everything fail a saving throw is cheesy enough. So while sanctum spell is nice, I dont want to consider 4th level spells for this.

[JDL]

You'll find most low level spells don't have total "save or fail" effects, since that wouldn't be within their power level. I'll address the SRD versions for Cleric since I don't have time to do Wizard too, but there's plenty more outside this list. Check sourcebooks like the Spell Compendium or refer to individual class handbooks for additional suggestions.

Cleric

Level 1

Bane
Save: Will
Duration: 1 min/level
Multiple Target: Yes
Effect: -1 on attack rolls, -1 on saves vs. fear
Verdict: Underwhelming. Enemies can still take move and standard actions as normal. This effectively raises your party AC 1 point against their attacks, nothing more.

Cause Fear
Save: Will
Duration: 1d4 rounds or 1 round
Multiple Target: No
Effect: Frightened on success, shaken on failure
Verdict: Too short. Good to take a single target out of the fight but doesn't last long enough to be worth spending your turn on.

Command
Save: Will
Duration: 1 round
Multiple Target: No
Effect: Variable
Verdict: Too short. If the target was made helpless, this would be a useful spell. Your best bet is probably to make the target fall prone to lower their AC and provoke AoO when they stand.

Doom
Save: Will
Duration: 1 min/level
Multiple Target: No
Effect: Shaken
Verdict: Lasting more than a single round is probably its biggest feature, but most fights are over in three rounds anyhow.

Level 2

Calm Emotions
Save: Will
Duration: Concentration (1 round/level)
Multiple Target: Yes
Effect: Halt combat
Verdict: This is actually a fairly good situational spell. If you happen to get ambushed and need breathing room, chuck this out and hold back the fight until your team can get their defences up. This spell essentially buys you actions in combat, which is what it's all about.

Enthrall
Save: Will
Duration: 1 hour or less
Multiple Targets: Yes
Effect: Halt combat
Verdict: See above. This spell has a wider range but far more ways the opponent (or your teammates) can break the effect.

Hold Person
Save: Will
Duration: 1 round/level
Multiple Targets: No
Effect: Paralyzed
Verdict: Good. Only works on humanoids, but anything that fails their save is almost guaranteed dead via coup-de-grace. Getting it a level earlier than Wizards doesn't hurt.

Silence
Save: Will
Duration: 1 min/level
Multiple Targets: Yes
Effect: Silenced
Verdict: Good. Take an enemy spellcaster out of the fight. If you target the caster they get their will save, which is almost always a good save for them. Targeting the ground around them prevents this but means they can walk out of the effect. Targeting your ally that's in their face with three feet of sharp metal is better. Targeting your summoned creature that's grappling them is best. Whether you can target it on your own Spiritual Weapon spell and have it automatically follow the enemy around is debatable.

Sound Burst
Save: Fort
Duration: Instantaneous
Multiple Targets: Yes
Effect: Stunned for 1 round
Verdict: Stunned is a useful condition since you deny the opponent Dex to AC and they drop their held objects. Sadly, the ones you want to drop stuff are the guys holding pointy things who have large Fort saves. Not terribly useful.

Level 3

Bestow Curse
Save: Will
Duration: Permanent
Multiple Targets: No
Effect: Variable
Verdict: Without a way to deliver this as a touch spell from range, it's fairly pointless. Use it if you win initiative or don't use it at all. The effect is very good, but it's also quite a high level spell to use on a single target.

Blindness/Deafness
Save: Fort
Duration: Permanent
Multiple Targets: No
Effect: Blindness or Deafness
Verdict: Always use Blindness, and target enemy arcane spellslingers. Bingo, they're out of the fight. Good range too. A solid spell, but only one target at a time reduces the effectiveness.

Contagion
Save: Fort
Duration: Instantaneous
Multiple Targets: No
Effect: Disease
Verdict: No. Just no. A waste of time in combat.

Overall Cleric Verdict: They're just not built to do multiple target crowd control well at low level. Keep a few Blindness/Deafness and Silence spells prepped for your enemy casters and Hold Person for the BSF.

[Crake]

Sanctum Spell'd Dominate Person.

The reason why is obvious.

"Oh, it's not really level three," you say?

It is if you scribe it as a scroll.

If this is the case, then does a maximised fireball wand cost the same as a regular one, since they're technically the same spell level? Or do you take the common sense route and say it's the spell slot that matters for item creation

[Deox]

Spells 3rd and lower that can (and often will) ruin someone's day:

1st -
Color Spray
Seething Eyebane (BoVD)
Sleep
Wall of Smoke (SpC)
Grease
Power Word: Pain (RotD)
Silent Image

2nd -
Blindness / Deafness
Cloud of Bewilderment (SpC)
Ghoul Touch
Glitterdust
Lam's Finger Darts (BoVD)
Phantasmal Assailants (SpC)
Pyrotechnics
Shadowspray (SpC)
Web

3rd -
Curse of the Putrid Husk (BoVD)
Deep Slumber
Flashburst (SpC)
Great Thunderclap (SpC)
Major Image
Mesmerizing Glare (SpC)
Nauseating Breath (SpC)
Shadow Binding (SpC)
Shivering Touch (Frostburn)
Stinking Cloud
Vertigo Field (PHBII)

[Extra Anchovies]

How has nobody mentioned Slow (http://www.d20srd.org/srd/spells/slow.htm) yet? Limiting one baddie/CL to a single action each turn is an encounter-ender, especially at high levels.

[eggynack]

The most devastating, though perhaps not the most powerful, is likely the corrupt spell touch of juiblex. It's a third level fort save against inevitable death within four rounds, stoppable only through the speedy casting of a small number of spells. The enemy can certainly kill you in the face in that time span, but if you just want an enemy dead out of a third level spell, touch is the spell for the job.

[Rubik]

Does Power Word: Pain count, since there's no save?

[ZamielVanWeber]

Does Power Word: Pain count, since there's no save?

Only if you can outrun the baddie afterwords. That spell takes a while to kick in.

[HJPotter]

Honorable mention goes to the 3rd level spell Unluck. An offesive Divination that makes the baddie roll its rolls twice, and take the worst result every time? It can be devastating. It's from the Spell Compendium, targets Will, and it does have SR.

[Werephilosopher]

My personal favorite is great thunderclap - targets all three saves, and each one has a decent effect. Will - stunned for one round, reflex - fall prone, fortitude - deafened for one minute. Plus it affects multiple targets, and doesn't offer spell resistance. The only downside is that it can't stun enemies that are already deafened, so if it fails the fortitude save the first time the second casting won't be as effective.