I also find the car a good way to get DD to sleep when she is really unsettled during the day. I usually try rocking/singing but if after a few hours things aren't working I jump in the car because once she gets overtired, it becomes near impossible to get her to sleep. The movement, white noise and music sends her to sleep pretty quickly but I know some babies simply hate the car.

I also found the brisk walking more effective then slow, gentle rocking. I remember I was rocking slowly with DD for what seemed like hours and then I thought maybe she was cold so walked with her quickly to the bedroom to get her sleeping bag but by the time I got there she had fallen asleep!!