I started with mapmyrun and a stop watch. I came up with a couple loops, 2 mi, 3 mi, and a 5mi. Then I knew where each mile marker was from mapmyrun. My stop watch had a "lap" feature on it so I could tap that at each mile marker.

Now I use the forerunner 305, and LOVE it. I still use mapmyrun to plan new running routes.