I use Fertility Friend. I haven't tried other sites because I have been happy with that one. They send you a free course through email that explains everything realated to charting. If you don't have a BBT they sell them at Rite Aid for around $13. My first mistake with charting was not taking my temp at the same time each day. Then when I decided to pick a time and stick to it, I picked 8:00am. Big mistake...LOL I always woke up at least once before 8:00 even if it was just to roll over. It made my chart a little hard to read. Now I temp at 7:00am and that seems to work pretty good. You really want to pick a time when you are most likely to be woken up by your alarm from a deep sleep.
Charting is a lot of fun. It's nice to get a picture of what your body is doing when.