I thought that Google Tasks interacted with Google Calendar. Doesn't that do what you want?

I've actually abandoned the gTask app for the mobile Google Tasks web site, but I don't need what you need, so I'm sorry, but I'm not sure what to recommend...

*edit*
Although, now that I think about it, Email to Self is how I do exactly what you're talking about. If you practice inbox zero, you're constantly annoyed by an email sitting in the inbox, and it reminds you every time you check your email to take care of that task. That's how I handle it, at least...