A handy website called Memo To Me lets you create reminders that will be sent to you on a schedule that you define.  For example, if you need to be reminded every Tuesday evening at 6pm to put the cat out, with a follow-up warning at 7, the site can do that.  Or if you need reminding that March 3rd is the day of your friend's birthday, it can do that too, by sending you a reminder each year in time to send a card.

Everything is very configurable, and you can attach additional notes and messages to the emails.  So whether you need a one-off reminder, or to set up something on a weekly, monthly or yearly schedule, check out www.memotome.com to sign up.  Everything is browser-based, so there's nothing to install.  And the basic service is free to use.