The recent Time magazine mentioned that one way for newspapers to make money online would be to have a very simple payment method (they mention something similar to ITunes) where one could pay online to read an article in a paper, or pay a bit more to read the paper for the day. You wouldn't have to commit to a subscription, but could make use of the paper's writing when desired. This makes sense with a newspaper or magazine where you know what to expect.
How could this work with other online writing? It's far more difficult with blogging. For instance, Breakfast with Pandora discusses the writers at Online Salon. It would be possible to get a community of bloggers together who decide to (somehow) charge for access to their blogs. If the writing was good enough, overall, or topical enough (sci-fi blog community, food blog community, etc.) that might be possible. You would still have to allow for, say, a free trial period, because the blogs would be unfamiliar. You wouldn't want to buy a pig in a poke.