Is there a champion that can outrange turrets without Firecannon?
All turrets have 1095 sight range and 775 attack range[1]
So the question is: are there any champions with an attack range higher then 775.
Each champion begins the game with a particular base autoattack range. This can vary from 125 to 200 for melee units and 400 to 650 for ranged units. The highest base autoattack range for champions is held by Caitlyn. At level 18, the highest autoattack range is 669 held by Tristana surpassing Caitlyn at level 16 with 650 autoattack range. This is because of Tristana's Draw a Bead.[2]
Sounds like there is no one with a base basic attack range higher then 775.
However:
Twitch's Rat-Ta-Tat-Tat increases his attack range to 850 from 550 for 7 seconds.[2]
So Twitch's ult should be able to out range an turret.
I have no tested this.
EDIT: gnarly 404 just tested this.
Source:
[1] http://leagueoflegends.wikia.com/wiki/Turret
[2] http://leagueoflegends.wikia.com/wiki/Range
Senna, as of patch v10.20, can damage a turret outside its range with enough Absolution (passive) stacks.
Considering a turret's attack range is 750 and Senna's base attack range for Piercing Darkness (Q) is 600, it takes 120 Absolution stacks to have the same attack range of a turret and 140 to outrange it, since Senna gains 25 bonus range for every 20 stacks.