Galio - Super easy to play but mana management is difficult at first.
Cho'gath - My personal recommendation. He might be a little awkward at first but I believe he is the easiest solo laner to play right now who is also EXTREMELY effective. You can build him full tank, hybrid tank + AP, full tank + Hydra, or even a zz'rot portal rush if you are familiar enough with him. He nearly works with any build. Full AP is a thing on him too because his AP ratios are out of this world.
Morgana - Very easy to play while being able to wave clear from a distance. She is a very passive laner though. Especially with all of the assassins coming out in the later patches.
Vladimir - Very easy to play once you get passed the small learning curve during the early game phase. All you really need is a lot of AP and his passive grants him more health for every point of AP you have. This makes building him a pure AP mage very easy to do. He is also one of the most effective at escaping ganks of the champions that I listed.
Cassiopia - Little more difficult to play than the others only because you have to be good at kiting with her E. Other than that she is really easy to pick up and has game changing potential with her ult.
Malzahar - Easy to play once you get his Q down. The only other thing you would need to know is how to manage his E properly so you never run out of mana.