I cut my rudbeckia back today, but not all the way, since I still have a few blooms. I basically did a serious deadheading. I'll do the final cutback after the first frost.
Fall is a good time to transplat or divide most perennials, although some should be done in the spring. I do most of mine a few weeks before the first frost so they have a little time to get acclimated before it freezes.
"As a general rule, plants that flower in the spring and early summer should be divided in the fall. Plants that flower in summer and fall should be divided in the spring before new growth is too large."
http://www.lewisgardens.com/prop&dividing.htm
You can do a google search for specific plants. Have fun!