I'm a fan of Noto by @kane which does the same thing but the swipe left/right interaction is delightful and quickly allows you to setup 2 different emails addresses or subject lines for different email reminders.

I know it sounds silly, but one product I use almost all of the time during the day is a product called Captio. I found out about it from David Tisch a few years ago. It basically makes it very quick and simple to send emails to myself on the go. I use it to jot things down quickly and I turn them into full-blown tasks later: