If you are going to seriously track weight changes, I have a few recommendations:
1. Pick up a set of scales. You can pick up a basic digital scale from Wal-Mart for $20. Even these low end scales are better than what most doctor's offices have and certainly better than many health club scales.
2. Pick a time and frequency to weigh and stick with it. Your weight will regularly fluctuate up to about 5 pounds per day. I weigh in first thing every morning, but I only log it once a week. Monday morning is my official weigh in for the week, because it keeps me honest over the weekend. Sunday is my hardest day to fight cravings. First thing in the morning is not usually my lowest weight all day, but it is the most consistent.
3. Keep a chart of your weight loss. You can do this in Excel, a exercise tracking like mapmyride.com, or (gasp) using pencil and paper. There is nothing like seeing the actual pounds lost on paper or computer screen to help motivate you.
4. Tracking weight is actually a poor weigh to measure diet progress, but it is the easiest, so I still recommend it. Just remember to watch for other cues as well that things are going well. Things like increased energy, looser fitting clothes, better sleep, etc. re all great signs that the changes you are making are doing what you want them to.