An “in-your-face” to-do list app for iPhone??

I know there are a bunch of iPhone/iPad personal organizer types of apps, but I need one that puts things right in front of me according to times I set. I need an app that, just like when you’ve missed a call, will tell me what I have to do by such-and-such a time when I wake my iPhone or iPad from sleep. This immediacy is critical for me, as I’ll forget to look at my list otherwise (!). Any such apps that you or anyone else can recommend?
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John Russell