I use followupthen.com as my tickler file. It is a pretty basic and easy to use service. You send things to the site with a date like email@example.com or firstname.lastname@example.org. On that date you get sent an email back with whatever you sent to the website.
Since about 90% of my tickler stuff comes from email this is a great way for me to have things that have been sent to me appear in my email box on the day I need to act on them.