All for one, and one for all!
Summon Monster (all of 'em!) - Just ask any rogue who got off a sneak attack due to a well-timed summon monster, or a wizard who got carried to the top of a cliff with a flying monster, or a sorcerer who had a summoned dire rat distract a guard while he mage handed the keys back to himself.
Shatter - ask the bard who saved the entire party's bacon by shattering an hourglass that ran a room trap (the DM had a D&D movie fetish).
Endurance - I survived a battle once at my Cleric 7th level, with 5 hit points left - and I had just cast endurance before we entered combat.
Keen Edge - The ranger thanks the party mage for making him a scabbard that casts keen edge on his rapier just before the start of combat.
Gust of Wind - a villain is perched at the top of a windy cliff, jabbering about how he is going to destroy us all. I'll let you fill in the blank.

Dream - Beats the hell out of Federal Express.

Tenser's Floating Disk - the guy who posted the train of wizards riding one another's tenser's floating disks while bombaring stuff below gave me the scary shakes.
Rary's Mnemonic Enhancer - Who wouldn't like extra spell power - and a 3rd level pearl of power costs waaaay too much.
Erase - I haven't tried it, but It would make a great practical joke to play on a wizard - erase a page of his favorite 9th level spell!
Got any more?