Action file as an alternative to the tickler file
I've tried tickler files before but find that something I read about years ago, and called an action file (or activity file??) works better for me. Instead of a series of file folders labeled for each month and a set for each day of the coming month, I have a set of file folders labeled for each letter of the alphabet, from A to Z. When I have a something I want to "mail" to myself to arrive at some future date, I place it in what seems the appropriately-lettered folder. For example, if it is a letter from the county that I need to deal with on a particular day in the future, I may place it in the file folder labelled C (for county?). Then--since I use Outlook with the GTD add-in--I will either make a task with a due date for that particular day or make an all-day event for that particular day. It might read something like "file declarations with county, AF-C" where the AF-C stands for "Activity File C", reminding me where the documents are.
There are a few advantages of this system over a tickler file. If I want to retrieve the document before it gets "mailed" to me, I will likely know to look in activity file C. If I can't remember which folder I placed it in, I can do a quick search in Outlook (I use the GTD add-in) and find the task or appointment. And since I use a Palm synchronized to Outlook, I will have the information with me even when away from the office.