...and I bet you will forget one.
EDIT:
It's not: Nasus Veigar Sion Bard Thresh Kalista Kindred Taric % health damage (too common to be considered a 'true infinite scaling ability', even though I concede it technically is)
Malphite.
If two Malphites Q eachother with perfect timing, they can achieve any amount of movement speed they desire. The only limit is how long the minions take to kill your base.
Sion, Nasus, Thresh, Bard, and Veigar [slayer-pantheon-thumbs]
hmmm.. Taric gives an armor aura to his allies that scales with his armor. Then in all for one game mode wouldn't the 5 tarics buff eachother to infinity?
Taunt Duration.
Trundle. His ult will scale infinitely off of other's stats.
chimes
passive stacks
pimp cane
HP passive
soul armor _& AP :) _
AP on q
and of course any %HP damage against sion, trundle ult against thresh, morde ghosts, yorrick ghoul etc... who aren't exactly infinity scaling themselves but in principle could on infinity scaling targets. Gold earning passives are also limited by item slot efficiency.
Do you mean like nasus and veigar?
Hey, you guys forget 
Also 
?
any champion with % of hp damage, since sion can have infinite health and any %hp damage upon him would also scale to infinity
Only other one I can think of is 
Do you count champs like ryze who scale from mana by using mana charge?
sion, nasus, thresh, bard, veigar, and kindred. this is all. As for the others on your list taric is a no. kalista is a no.
what about 
and 
? their passive
