Herb gardening is all about timing and cycles. We have a zone 7 garden, and late summer and fall can be a bit of a slump in terms of harvesting.
Generally, herbs harvested for their leaves are best harvested right before blooming. If you have been pinching back the tops on your herbs to delay bloom and encourage the plants to fill out and produce more leaves, some of your herbs may almost be ready for harvest.
For the most part, though, this is a slower time when most of the annual herbs are spent and a few perennial herbs are either coming into a second bloom after a first harvest or just getting ready to bloom for the first time. Most perennial herbs have completed blooming for the year and are already focused on building up their roots for the coming winter.