Don't Forget Anything! (Auto Reminders)

You know those nagging feelings that occasionally make themselves present until you finally follow up on something?

I had been having a set of those regarding my car registration for a couple weeks before I finally remembered when I was by my car to check my expiration date. I know, I know—this is a simple thing to check, but it would only cross my mind when I was far from my car. And when I say "far," I mean not immediately inside or standing outside the car. 

So I wasn't exactly surprised when I saw my registration was expired. Great. And I admit this happened to me last year as well. Turns out, if you don't move every year, you might actually get the renewal notice in the mail. 

I've got everything squared away, but this whole ordeal made me think of how I can best set up automatic reminders for things just like this. 

Google Calendar Reminders

If you are an avid Google user like I am (Gmail, Reader, Music, Play, Calendar), a Google Calendar reminder is a pretty safe way to go. I'm a little leery of relying on apps that I might not be using months from now. So, I've set up a reminder for the beginning of December for myself to get my registration on my radar. This will send me an e-mail and pop up on my account until I completely dismiss the reminder. Now I can sit back and relax about the issue until then. I've also set up periodic reminders for rent and phone payments, to check certain accounts, and for tracking personal goals.

Question: What apps or resources do you use for reminders or to help manage tasks?