Google introduced in Dec. Gmail Tasks, now the team has released an optimized version for your iPhone or Android device to let you manage your task list any xhtml enabled phone. Just go to gmail.com/tasks from your phone's browser and log in. If you have a Google Apps account, you can go to mail.google.com/tasks/a/your-domain, replacing your-domain with your actual domain name. If you already use the version of Tasks in Gmail Labs, you'll see the same task list that's always in sync. You can add new tasks and check off completed ones.
Google also launched an iGoogle gadget that provides similar functionality. The gadget is only a wrapper for the standalone version available at http://mail.google.com/tasks/ig, a page you can bookmark or add it to your sidebar in browsers that support this feature (Firefox, Opera).