decent amp sim on iOS?

[kvotchin]

And hopefully cab sim too. Must be an AUv3 plugin.

Anything good on iPad/iPhone that will do that stuff?

Clean through to high gain, preferably.

[mindnoise]

if you need AUv3 then your options are Nembrini or Yonac Tonestack Pro (not 3!).

Nembrini is awesome, though I am not a guitarist.

Sometimes Yonac have a deep sale on the Tonestack "Pot o' Gold"-IAP which gets you everything the App has to offer.