I just used flot a few days ago and was really impressed. Especially with how it does time series so easily. You just hand it a bunch of dates, which may includ

I just used flot a few days ago and was really impressed. Especially with how it does time series so easily. You just hand it a bunch of dates, which may include irregular intervals or gaps, and it figures out a reasonable representation for the data so it looks consistent. Really really nice and simple to use too.