Tombo

A freeware, lightweight, hierarchical notepad app. Development is (very slowly) ongoing but although the latest version is in late Beta the previous version works very well.

Pros

• Lightweight
• Free (and open source)
• Regexp searching
• Virtual folders (group any document with a specific keyword)
• Optional encryption
• Versions for Windows Mobile and (third party) Android
• Data saved as a folder/file structure so easy to sync part or all.

Cons

• No markup capability (RTF or HTML support would be great) although it can open up another program of your choice to handle these.