What I consider the best is HeartWatch.
Although it's name implies it's for the heart it also works excellently in storing regular heart beats, workouts and sleep patterns; all shown on the Watch.
I use sleep++ also. I also have HeartWatch which I use for HR monitoring as I have an irregular heartbeat. The sleep part of HW gives different results to Sleep++. Not sure which is more accurate or whether they really should just be used as a relative thing anyway.