All you have to do is add an account to a private list (without following them) and then view the timeline for that list. I really only ever interact with Twitter through Tweetbot (tear today!) or Tweetdeck, so I have one list I call "The Group" that is a highly curated list of folks I actually want to see stuff from, and a few other lists of accounts that are intermittently interesting but that I don't need to actually follow.
Because following an account is akin to an endorsement or at least a weak association in a way, this method is also interesting when it would be useful to stay updated with an account without strictly associating it. (Some will immediately think of political accounts or counter-culture accounts; I actually use it when following companies that I might need to see news from like my utility but that I don't want to say "Hey spam me with your PR!")