Twitterrific 2.0 for iPhone allows you to customize exactly which types of tweets you see in the unified timeline. It can combine tweets from people you follow, mentions, and DMs (Direct Messages) in one stream but also still display them in separate areas.
This is quite handy if you run some kind of customer service or parody account. You can feel free to follow your followers in order to interact with them via DM, but only choose to display mentions and direct messages in Twitterrific if that’s just what you need to see.