I use an excel workbook to keep track of things, including actions or to-do's, my server names and specs, software billing to departments, projects and status, communication plans, registration of risks and issues, training plans, staff duties, projects plans and pretty much anything else that has to do with GIS management. I even learned how to create GANTT charts in Excel from the internet.
Sometimes after a long weekend it helps to get right back to productivity. It also helps me to plan ahead - I would not some bigger to-do items late in the afternoon or on a Friday, I'd work on clearing out smaller to-do items and maybe cleaning up my office/desktop and start the bigger tasks that require more focus on Monday or Tuesday morning on a week when my calendar is relatively clear.
That's my method - I copied it from another successful project manager and it works well for me. What's your method for keeping up with the to-do list at work?