While I have no particular champion I find weaker than the others (I haven't read all the lores and don't remember all of them), I disagree with alot of the ''weakest'' champions you guys have brought up. To all of you saying Nunu or Corki or Heimerdinger are the weakest because without their yeti/plane/turrets they are nothing, well by your logic all melee champions that use weapons are among the weakest because without their sword/w.e they are just physically fit people who can punch stuff, and ranged characters without their guns/bows can't do ****. Mages could still cast spells without their staffs so they would be overpowered. Basically, you cannot ignore the champion's assets if you want to decide which is the strongest/weakest.
Also, regarding Soraka, a very small fraction of a god's powers is still alot of power, no?