Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
Documents by Readdle - A central hub for all your files.
TeXworks - The TeXworks project is an effort to build a simple TeX front-end program (working environment)...
Documents Pro 7 - The ultimate all-in-one mobile office suite for the iPhone and iPad with 8 premium apps in 1.
Texmaker - Texmaker, free cross-platform latex editor
GoodReader - With GoodReader on your iPhone, iPod Touch or iPad, you can read virtually anything, anywhere.