Legions:
Amplify (crappy mechanic anyway): show your hand as something comes into play and put X+1/+1 counters on the creature for every one you choose to show (with the same creature type).
Provoke: Attack and you can force one creature to block it (so YGO, ugh). This is similar to cards like lure, but isolated.
Double Strike: Creature deals first strike and normal damage
Scourge:
Storm: When you play the spell, calculate how many spells have been played (copies don't count). Make that many copies of the spell with storm on the stack.
Landcycling: Best mechanic from scourge IMO, instead of drawing a card (cycling), you search for a land and put it into your hand (e.g. plainscycling gets you plains).
Mirrodin:
Imprint: this is the process of removing something from the game under the card's ability. this card usually does something with the imprinted (removed card), like copying it or using it to give the thing flying...
Equipment: It's like an enchant creature, but it stays on the field when the creature dies. It tends to cost double (to play and then equip) of the local enchantment, tho.
Affinity: You pay 1 less for every [something] you have, let it be artifacts, lands, etc., to play the spell
Entwine: Choose one of two effects, or pay the entwine cost to do both
Darksteel:
Modular: Remember the chimeras? They're back (sort of). When a creature with modular dies, you can move its +1/+1 counters over to other artifact creatures (so you waste nothing).
Indestructable: Anything that destroys it or anything that gives it lethal damage will not kill it. Removal, bounce, and state-based kills (e.g. -1/-1) are still valid to "kill" them.
Good stuff:
Legions:
Akroma, Angel of Wrath
Phage the Untouchable
Scion of Darkness
The Slivers
(I don't like this set too much, it's all creatures.)
Scourge:
Decree of Justice
Decree of Annihilation
Eternal Dragon
Silver Overlord
Forgotten Ancient
STIFLE!!!!
Mirrodin:
Broodstar
Guilded Lotus
Platinum Angel (you can't lose the game)
Icy Manipulator (is back)
Soul Foundry (make copies of creatures...good ones)
Mindslaver (take control of target opponent)
Auriok Steelshaper (cheap equipment)
Fireshrieker (double strike!!!)
Leonin Skyhunter
Pentavus
Myr Incubator (known as the extended breaker when tinker was around)
Ishron Scepter (most valuable uncommon in Mirrodin)
Darksteel:
Darksteel stuff (Collosus and forge in particular)
arcbound stuff (reclaimer and crusher being the craziest)
Blinkmoth Nexus (known as Darksteel Mishra's factory)
FIREBALL!!!!!
Memnarch (says: 4UUU: take control of target permanent)
Reshape (tinker weakened)
Panoptic Mirror (copy sorceries/instants)
Serum Powder (alternative to mulligan)
Vedalken Engineer (a common that is highly drafted by many)