I'm not really familiar with the parts of Google Reader that weren't just viewing RSS feeds, but have you looked at NewsBlur? I believe it has an API for apps and it has some sort of social network.
I'm going with Feedbin (https://feedbin.me/) and the iPhone version of Reeder (http://reederapp.com/iphone/) for the moment. Feedbin's web GUI is very simple but there's hope for progress. And the Reeder developer announced that he plans to add Feedbin support to the iPad and OS X versions of Reeder (http://reederapp.com/reader/). As a backend for syncing feeds with Reeder on the iPhone, Feedbin has been working well for me so far.
(BTW, Feedbin has no official trial but you can use it for three days without getting charged on your credit card.)