One of the first things I do is to browse the web, just looking for some beautiful pictures.
On one hand this could be somewhat counterproductive if you both lack inspiration and at the same time is a bit depressed because of this. Then thoughts like "Wow what a beautiful picture - I can never achieve something nearly as good" But on other hand you can think "Wow what a beautiful picture - I wonder how he/she achieved that. How can I achieve that with my equipment? Right now I've been watching some of von Wong's youtube channel and I have to say, he is a great source for inspiration.
Sometimes it's a good thing to go on a walk in nature not thinking about angles, composition, what would be a great picture, gear, camera settings etc. Just go out and enjoy nature and all it's beauty. I've still not seen any photo that trump nature.
If you don't have to consider money, go out, buy some new equipment like a new camera, a new lens, filter or something else. Or take a photo workshop in a foreign country.
If you are like me and don't have limitless amount of money, choose gear that limit your shooting. Like only bring a 50 mm lens. Or a even more challenge choose a fisheye or a 400mm lens.
Join a community with specific topic, perhaps a topic that is outside your comfort zone. Like if you mostly shoot landscape, join a beauty shoot community or the other way around.
I've joined +The Arcanum and I'm in +Glenn Guy cohort. There I get a lot of inspiration, mostly from my fellow cohortians but also from other people in The Arcanum both masters and people in other cohorts. And this hangout thing on Google, what a great thing. I can sit up here in the north of Europe having a video call with people from all around the world, talking about photo and everything there around.
There you have some of my source to inspiration. Now, please enter some of your idea's in the comment field.