A post I read at Masked Admirers gave me insight on cards that have been great in my cube and I did not know or had not considered. I'll try to be as useful to you as that post was to me by sharing my experiences with individual cards that surprised me.
This expensive enchantment helps immensely when you are racing with your opponent. It also slows down aggressive decks by effectively reducing their creatures' power by 1. In the long term, it may net you a huge amount of life, and it shines in multiplayer games.
While it is true that it cannot target most creatures, it can hit the ones that matter most. At two mana, it's typically a nice tempo swing, and I'm still yet to see a game in which it was useless.
This guy excels both in attack and in defense. A 1-drop, meaning it can hit the red zone on turn 2 as a 3/3, taking out even 4-6 toughness blockers in two turns. It can also be a 3/3 blocker for G however, and one that will, when chump blocking a fatty, make it much smaller.
This fills two roles a blue control deck needs with one card - it's a counterspell and a finisher. And not all finishers can be cast during the opponent's turn.
Probably the best black control card. It usually nets card and tempo advantage at the low cost of three mana. It wins games against aggro by itself.
Without the mana burn rules, it's not a 3/3 for 3 mana that can be played in any deck. This is better than any color besides green gets for that much mana. Also, it may help ramping into something huge with a sacrifice enabler.
The red permanent Last Gasp, for one extra mana. Versatile, it can be used as a combat trick make an attacker small enough for your blocker to kill and survive, to kill a medium-small creature (regenerators and indestructibles included) or just deal the last 3 damage to the opponent.