Drafts from Agile Tortoise is the ideal digital notepad for the person who wants to capture a thought before it's gone. It has a simple UI that doesn't get in the way of its primary function, which is jotting down notes.
The app opens to an empty draft that's ready for you to record your latest thoughts, type out the draft of a tweet or prep some markdown code. Drafts's emphasis is on quick and easy notes that can be shared on Twitter, email, or copied to the clipboard. It also supports markdown so you're not limited to plain text.
Drafts has several small but handy features. The app keeps track of both your word and character count, which is extremely useful when you are composing a character-limited tweet or a text message. There's also a search function that'll help you find the important note you created last month. If you own the companion app Terminology, you can highlight a word in Drafts and easily look up its definition and usage.
Drafts is available in the iOS App Store for US$0.99. It works on the iPhone and requires iOS 5.0.