Here's a few tactics.
Fog Cloud/Solid Fog + Rogue or Ninja with blindsense/tremmorsense. In fact, any spell that makes them blind while the Rogue can see = nasty. DMs, take note, you'll have more Rogues than the PCs will.
Ethereal Rogue with Ghost Touch weapons. Plus nondetection of course, better than invisibility since most things won't be able to hit you back. Heck, whack an Improved Invisibility on to to make the weapons invisible too. Tactic for mooks only, though, any BBEG worth their salt has True Seeing.
Maybe not exactly a tactic, but a certain Rogue build I used effectively was a Rogue/Ranger focussed on duel wielding thrown daggers and shuriken, combined with Invisibility/concealment/HiPS/cover/whatever. In cramped dungeons, 30ft can be a loooong way, the real trick is staying mobile and out of sight.
For spellcasters: Flight/Protection from Arrows, etc./Wind Wall/ranged damage spells.
Mystic Theurges and Clerics can really surprise opponents with Divine Power + Ray spells. Fighter BAB making ranged touch attacks, particularly with Polar Ray or Meteor Swarm.
Speaking of Cloudkill and Mystic Theurges, though a tad off topic, the high-level cleric damage spells are unbelieveably nasty, considering they can have enormous areas of effect. Earthquake, Tornado, Fire Storm, Elemental Swarm... Makes the wizards feel a little obsolete at times. Oh, sorry, Shapechange into draconic form, almost forgot that drawcard.
Telekinesis +Trap or Environmental Hazard. Situational, sure, but lava and green slime are still favourites. Also good for pushing interesting objects (heavy rocks, barrels of oil or Dwarven Ale) onto enemies below. Also, Telekinesis + unstoppered vial of contact poison. Lots of fun, depending on the poison. Or, any ideas on creating your own environmental hazards and tossing foes into them? Lots I'm sure.
Contingent area effect spell + Unintelligent or chamed/dominated creature. Create your own suicide bombers, trick is to craft the contingent effect so that the charmed creature doesn't know what it's doing. Skeletons that go boom an old favourite. For those of us who are evil, charm the target's nearest and dearest...
Um, speaking of tactics, can anyone think of anything that a fighter can do that really counts as tactics? I mean, most fighters that I know of soak alot of damage and hit things hard, or at best (tactics wise) tie up powerful creatures while the spellcasters and rogues dish out the real pain.
Monks too... other than 'caster killer', it's hard to see a point to them tactically, though that's not a bad tactic in itself. I guess a Rogue and Monk working in tandem, the Monk attracting attention while the Rogue flanks or snipes is viable. In fact, Monks flanking makes for good co-operative tactics on the whole.