I've rediscovered my itch to knit. And, who knew, the answer was so astoundingly simply I'm surprised I didn't discover it before. I'm sure I'll pounce on it quickly from now on.
The way to kick myself out of a knitting slump, I've found, is to buy more yarn.
I know this sounds like a thinly-veiled excuse to further expand my stash, but it really worked. When I have a new skein of yarn, I immediately start thinking of what patterns would work with those yarns, and all the things I could make with them, and on and on, and then suddenly I want to make things with them, but to do that I have to finish what I'm making now, and bang! just like that I want to knit again.
And besides. Everyone knows that sock yarn doesn't really count as stash.