Automatic spell check has been built into many browsers for years, but typos continue to plague even the most reputable websites (and print media, for that matter). Recognizing this fact, a number of services have emerged that will continuously monitor your site for spelling errors.
Spellr.us, currently in a registration-required beta, plans to offer hourly, daily, and weekly sweeps of your site, and will provide a visual snapshot of a page with errors clearly marked with strikethroughs. Their main competitor at this point is NetMechanic, which has been available for years but lacks any of the visualizations promised by Spellr.us.
This space is still in its infancy, but I can imagine that these services will be a boon to bloggers and other website publishers. The company’s current questionnaire alludes to a price range of around $50 – clearly a worthwhile investment for many sites. Keep a look out for Spellr.us in the near future.