With the coming demise of Google Reader, it's time to begin searching for alternatives.
There are two aspects to Google Reader: (1) it acts as an RSS aggregator or server; (2) it has a web-based client interface.
If you're using a single client interface to Google Reader whether it's the Google Reader web interface or single client app, like Reeder (iOS) or Press (Android), that pulls your feeds from Google Reader then the distinction between the client and server aspects to Google Reader may not factor into your considerations of alternatives.
However, if you like to use multiple client reader interfaces while keeping your read/unread and favorites in sync across all client interfaces, then you'll need to consider the client and server/aggregator aspects when looking at alternatives and there are far fewer alternatives.
I suspect (and hope) that there will be more alternatives as July 1, 2013 shutdown date approaches and I'll post here with updates.
There's a publicly maintained spreadsheet of Google Reader alternatives but it doesn't highlight aggregator solutions that provide an API for multiple client support nor does it specify what aggregators the client apps support. I'd like to see this spreadsheet split into a client and aggregator sheet or at least add a column specifying whether the app acts as a client or aggregator.
Marco Arment has written a good post on the Google Reader API situation. If new RSS aggregator alternatives add a Reader compatible API and the client apps add support for a hostname parameter, all of those client apps could work with new RSS aggregators without too much difficulty (authentication and feed organization would still have to be addressed).
As of this date, there are only a few potential options that provide a client API and I'll summarize them here.
Fever is a php/mysql application that you host on your own server for a one time $30 charge. It has a client API that has been available since mid 2012. The API is currently supported by the Reeder app for iOS devices and the Mac. Nitin Khanna has a nice post on how to install Fever on a free account with AppFog.
Feedly provides a promising alternative to Google Reader. It's an RSS Aggregator that has their own Android, iOS, Chrome and Safari client apps but they've also recently announced that they will be creating a Google Reader compatible API. This would make it much easier for your existing client application to work with Feedly.
The Old Reader doesn't currently support a client API but a few weeks ago they stated that this was their top priority.
Digg recently announced that it will be building a Reader and that they will support the Google Reader API.
Feedbin provides an RSS aggregator service and slick web interface for $2 per month. It also has a supported API and now has the backing of Silvio Rizzi's Reeder app for iOS.
Newsblur is an aggregator service and client app that has a free limited use version as well as a premium version for $24/year. They have both iOS and Android client apps that are free and they also have a supported API that was released way back in April 2011.
Besides tracking the aggregator alternatives directly, I'll be keeping a close eye on my favorite iOS and Android client apps. Here's a recent tweet from Press for Android on this subject:
And a couple of tweets from Reeder: