No one's said the magic word yet, so I'll bite: Freemium?

Replace the gray checkbox app icon with a smart looking man/woman winning at life all thanks to Platinum Tasks.

Give us a promo code to try it for free, so that we can post reviews.

Note in the search results for "Google tasks", a lot of the apps on the first page also have "to do list" in their names. Maybe yours should too.

See this discussion for more ideas - http://news.ycombinator.com/item?id=2768376

And don't give up. The thing with selling is, you've got to sell.