Here are ideas for finding new themes and subject matter for your next podcast:
If you're currently getting paid for your time and expertise, that's a good sign that you have something interesting to say on the topic.
For example, Christopher Schmitt is a web designer, so he talks about design on his show:
If you're already blogging on a particular topic, you can create a podcast where you read your blog posts. This is exactly what Ashley Baxter is doing for her Bootstrapped Digest podcast.
Also: look at when some popular shows were last updated. If it’s been months (or years!) you might be able to create a new show to fill that space.
One of the best ways to create new shows is to remix your existing long-form content.
Now, you're giving listeners the choice: do they want a 1-hour interview show, a 30-minute "commuter" show, or a 5-minute highlight show? You're remixing the content so it appeals to different types of listeners!