I am one of those guys who like to design in one, master, PSD. Re-using elements throughout so I can tweak them without re-implementing everywhere.
One thing I have been struggling with over the years is finding an easy way to show separate variations of designs. Until very recently, I have had to remember the different states, layer positions, and visibility of folders/layers. This is less than ideal since the next person who opens my PSD may or may not be able to figure those states out.
Just yesterday Steve Streza pointed me in the direction of Layer Comps. A, pretty hidden and under utilized, feature of Photoshop which does exactly what I have been looking for.
Open your Layer Comps window (Window > Layer Comps), adjust the positioning & visibility of the layers for your first variation, click "Create New Layer Comp" (little paper icon), name it logically and voilà. Repeat this step for all variations.
Whether you are designing in a single PSD or break your screens up into separate PSDs, I highly recommend using Layer Comps to show all the variations of your UI. This will dramatically improve the quality and organization of your PSDs. Reducing the ramp-up time for clients, co-workers, and just about anyone else.
You know you are organized when someone else can open your PSD without an orientation. Work smart.
UPDATE: Right after publishing this Wade Hammes mentioned you can even break these Layer Comps into separate PSDs (File > Scripts > Layer Comps to Files) at a later date.
I will be implementing a commenting platform soon.
Go connect to Twitter for early access when it's ready.