Anivia- Excellent team fight potential with her wall and ult, and her combo only requires you to land two skills.
Brand/Xerath- You really only need one of the two, as they play very similarly with their "combo your spells to stun enemies" kit and their "rape the entire enemy team with AoE" late game- Brand has the potential to do more damage with his fire-and-forget, team-destroying ult, but Xerath is a bit harder to kill due to his armor passive and tendency to stay back.
Kassadin/LeBlanc- AP mid assassins. Focus more on shutting down the enemy carry than carrying themselves, you should probably pick up one of these to counter big scalers. LB's burst is scarier, but Kassadin's a bit more effective late game.
Katarina- Poke. Poke. Poke. She's another good pick for shutting down really hard carries, and can actually do a pretty significant amount of damage late game as well. The only downside is that you'll probably die too, unless you have a really good sense of timing, or are really far ahead.
Mordekaiser- Manaless champ with a shield and decent poke. This guy can out-sustain pretty much anyone. His teamfight potential is fairly limited, but if he manages to land a kill on the AD carry with his ult, it's pretty much an insta-win.
Morgana- Not the most threatening laner, but her farm is really easy, and her utility late game is ridiculous between her snare, ult, and spell shield.
Orianna- The utility midder. Her passive scary, giving her almost the same teamfight ability as an ADC late game.
Ryze- Ryze's scaling is ridiculous. He can build tanky and still deal an impressive amount of damage during pretty much every phase of the game due to his abilities scaling off of mana. His downfall lies in the fact that he has no range and no mobility, meaning he's pretty unforgiving, and if your teammates don't engage well, you're not going to do much in a teamfight.
Twisted Fate- Difficult champion to play, he's squishy and his Wild Cards are easily dodged, but he's got a powerful ranged stun that also does significant damage, decent sustain with his mana refunding, and his passive and ult are great for helping out your team and maintining a constant presence over the entire map.