Tapatalk forum app for iPhone is now free.

I participate in a lot of forums:
imore
macrumours
digital point
ubuntu forums

and lots of others

I first found tapatalk a while back and I use it every day.
a few of the features that you’ll like:

iCloud sync:
Tapatalk remembers the forums you use and will sync your active forums across devices
It doesn’t sync the login details, so you will have to login on each device, but you don’t have to hunt down each individual forum or type in all of the details on each device.

Most visited forums:
Your most visited forums will show in the home screen of the app, allowing you to click through to each and see replies to posts, post new replies to others, add new topics, etc

Along with reeder for the iPhone tapatalk is one of the apps that I would highly recommend.
check it out on the app store for free now :D