Aleix contacted me about their new service, "Post or Pay":
Post or Pay is a website that allows bloggers to put a price to not blogging. The user sets a deadline for her blog post and a price. If she doesn't publish it on time, she pays.
20% of the payment goes to charity (the World Literacy Foundation).
I use Beeminder for tracking my blog posting. As long as I post frequently enough, I'll stay on target and not get billed. It's working well for my 30 Days of Blogging trial, although it wasn't totally painless to set up - I had to hook up my RSS feed to Zapier in order to automate data submission.
Post or Pay works a little differently; you commit to writing a single post by a specific date, and then send proof once it's published. It's a much more focused approach.
If you're struggling to blog more, or you're looking to dip your toes into the world of commitment services, Post or Pay might be a good place to start.