Cork

Cork is a reminder addon, aimed primarily at buffs. Cork was inspired long ago by NeedyList, and has been Alpha quality for years. Wrath introduces new buff query APIs that let me finally make Cork as small as I’d prefer, so I’m finally pushing out a beta-quality version. Cork provides, at it’s heart, one-click buff casting. Some non-buff reminders are included as well:

Reminders for self-only buffs, auras and shapeshifts
Reminders for raid-group buffs (ones that cast on multiple targets)
Reminders for warrior shouts only shown in combat
Priest Fear Ward (shows whenever fear ward is not on cooldown, must be manually enabled when needed)
Shaman Earth Shield (tracks the last group member cast on, so you must cast manually the first time)
Warlock demons
Warlock Soul Link
Low durability warnings when resting (in town)
Clam shucker
Minimap tracking
Keybinding (thanks cladhaire)
Macro-generating button

One-click? How?
Simple! Make a macro: /click CorkFrame. You might wish to add a /cast [combat] Some Spell at the start as well. You can also use the keybinding in the default k2eybind UI. Be warned, Cork will only cast out of combat. If you want to apply buffs in combat, you’ll have to do it manually.