Best exploit I've ever posted here, here it goes:
At christmas you get a pet called "Clockwork Rocket Bot". If two of them are summoned close to each other, they kill each other.
Now the thing is that if shadow priest's rocket bot is killed, it is counted as his kill. This means it triggers spirit tap! I have tried this 3 times, worked every time. So basically in raids you get infinite spirit tap mana regen if you just keep summoning the pet when tap wears off.
Long story short:
1. Have the pet on shadowpriest and some other guy.
2. When you want free mana, summon out the pets and gain Spirit Tap.
3. Rinse and repeat every 15sec
4. Profit
PIC:
Reason this isn't posted before is probably that the bot was switched to work just few patches ago.
Links to important stuff:
Clockwork Rocket Bot - Thottbot: World of Warcraft - The imba pet
Spirit Tap - Thottbot: World of Warcraft - Spirit Tap
TIPS:
This may probably work with other effects/talents that trigger from killing an enemy.
Even if you are a healer in raid guild, you could probably spec for tap if there is someone other with the pet too. 5 talents is cheap price from infinite mana.