View / sort Podcasts list by subscribed status
There doesn't seem to be an automatic sort option to send currently subscribed podcasts to the top of the list. I have the same complaint (among others) with the podcast capabilities of iTunes. There are a couple of ways you can do this manually though.
Create a station and only include the podcasts you are currently subscribed to in it.
In the "My Podcasts" view, click the "Podcasts" drop-down menu (top right) and sort by "Playlist Order". You can then drag & drop to reorder your podcasts in the left hand pane.
#2 is what I do. You can quickly see whether or not you've subscribed to a podcast when you select it - if you're subscribed it will say "Updated xxxxx" under the podcast title. If you aren't, it will say "Not subscribed" along with the last updated date.
A bit annoying, but it seems that this is the only option. There may be a way to generate a playlist using some scripting, but from looking at the iTunes library file I don't see any information in there that indicates whether or not a podcast is subscribed to. (Someone more familiar with scripting for iTunes may have a better idea here).