Circuit ideas are everywhere! There are many places to find cool circuits.
The greatest sources for my inspiration are hacker/maker/electronics blogs, schematic webpages, hobby project pages, and open-source hardware companies.
Or you can also check out some electronic kits for inspiration.
Sometimes I just want to try to replicate an electronic circuit I’ve found on the web. Either because it is something I need or just to prove to myself that I can do it. Like this amplifier circuit diagram.
Sometimes I find something cool that I want to modify and improve on. And other times I get completely new circuit ideas out of the blue that I want to build.