I have a Sony ICD-35. I mostly use it in the car so I can capture ideas while driving. It's very easy to use one handed.
I've been going back and forth between using it for capturing ideas at work instead of using my planner. My other idea is to use 3x5 cards and then rewrite my ideas. I'd then take the audio notes and enter them into my planner once I get home. (I use 2 planners, one for teaching and a personal one at home) This way, I only have to carry one of them.