Instead of creating a post and then scheduling it, Buffer starts with the schedule and then inserts your posts into it sequentially. (Prior to actual distribution, scheduled posts can be re-ordered.) Immediate posts and "normal" per-post scheduling are also available.
HootSuite gathers activity from numerous social networks into a dashboard display. Activity can be filtered into separate streams, and those streams can be arranged across multiple tabs.
In addition to Twitter, Facebook and LinkedIn, HootSuite supports many networks not covered by similar services; examples include YouTube, Tumblr, Foursquare and MySpace.
Friends+Me allows default distribution targets to be overridden with simple, customizable hash tags. This allows both omitting a target, and adding one that isn't in the default list.
AgoraPulse emulates the way email clients keep hold of conversations. All incoming conversations are in a folder called "Inbox". Clicking on a conversation will display the whole thread and allow you to respond to the conversations right there. It helps you make sure you don't miss anything.