A smartphone is a great tool to take notes because it is with us everywhere. There are many notepad apps for Android that fit the bill, but I have taken a liking to SimpleNote. This is from Automattic, the folks behind WordPress. It can be installed from the Play Store here.
In SimpleNote, you can keep multiple note files. The first line you type in each is shown as the title. Simple formatting options are available. And the best part is that by creating a login, you can have your notes synced across multiple Android devices! There is even a web app to check your notes when your phone is down.
Another trick I use is to share a link from Firefox on my PC to my Android device. I just paste the link in the web app of SimpleNote and copy it up on my Android device.