1) Add a couple more features that are geared around integration with people's workflow, like phone reminders, and maybe some ability to, oh, I don't know, send a grocery list to a husband, or a parts list to a delivery guy.
2) Research, research, research, where people are spending money on the internet for something like this. You'll find the usual suspects, like Basecamp, and you'll want to avoid being like that. Instead, you'll want to find underserved markets niches, dozens of them.
3) Once you've identified the markets, build a list of them, and outline the contents of a landing page for each niche. Do this on the computer, so that you can programmatically create all these landing pages and capture some of the long tail traffic.
4) This should really be #1, but get someone to start paying, anyone. This will force you to scratch someone's itch who has money. Make whatever changes they need so that the service is valuable to them. You really need to find one person out there, who's saying "I wish I had an online task list that met my needs! If I only did, I could make $X more this week/month/year."