[jeffmould]

How about Google Calendar or similar? When I freelanced I used a combination of Google Calendar for domain and cert expiration/renewal dates and used Quickbooks to remind me when those dates were as well for billing purposes. I had a separate calendar within my calendar just for these dates and would have Google email me with what was due that day and week. You could even tie Quickbooks in to automatically invoice your customers on said date to take the hassle out for you.