Hacker News Reader

Apollo is brilliant for iOS users.

Been using it since release and I don't use the Reddit website directly now except to give gold.

Relay is quite good, I have (shamefully) used it for hour-long browsing sessions.

I'll second this. I've tried other ones but I always end up coming back to Relay.

On android, previously I used RedReader but I have since switched to Slide https://github.com/ccrama/Slide/ (available on Fdroid).

It has a nice UI and a lot of neat features.

Check out Sync for reddit for Android [0] and iOS (Beta) [1]

RedReader is great and open source.