Check out Painless Software Schedules by Joel Spolsky, March 2000.

I am also terrible at estimates, and I tried his method for my latest project - it really helped.

Additionally, I track my time in a seperate sheet in Excel, breaking up my day into generic tasks - Meetings, Useful Meetings, various projects, Administrivia, Helping the New Guy, etc. So I end up with 2 views of my time - a long-term tracking of my time by day and how I tend to spend that time, and a per-project estimate of how I think I'll be spending my time in the near future.