Banned
Ancient Tomb and Sol Ring: Ramp that can be slotted in any deck. They basically turn the game into a luckfest where the one drawing their piece can pull ahead too easily.
The tutors and Tinker: Too powerful an effect for too low a cost.
Isochron Scepter: This card is just too easy to abuse with counterspells, instant-speed removal or whatnot.
Mana Drain: Counterspell is one thing. Counterspell that ramps is another.
Rhystic Study: Can provide the blue deck with an unparallaled amount of card draw.
Sensei's Divining Top: Provides unparallaled card selection. Also ensures games go to time since the actual rule box reads ": Add 5 minutes to any given turn."
Skullclamp: Can provide the token and aristocrats decks with an unparalleled amount of card draw. Also acts as a semi-sac outlet.
Swiftfoot Boots and co.: Hexproof seriously affects the ability of players to interact with the board. Especially equipments that also give a toughness boost, such as Mask of Avacyn and Mirror Shield, can make any creature virtually unkillable in a format where effective boardwipes are few and far between.
Treasure Cruise: Potentially Ancestral Recall at sorcery speed.
Watchlist
Archetype of Endurance: Resolving this guy in a format with precious few boardwipes or ways to deal with hexproof is in many situations tantamount to making your board virtually unkillable.
Ashnod's Altar: A great sac outlet that is integral in quite a few combo's. Easily provides infinite mana and segues into other infinite shenanigans.
Exsanguinate: Hard to interact with finisher.
Lightning Greaves and co: Shroud limits the interaction more symmetrically than hexproof. Combined with haste makes this card a formidable equipment. See discussion above.