I have been using JotNotes for years and find it invaluable.
You can 'try before you buy'. ($29.95)
Note: I have no commercial interest whatsoever in JotNotes. Just a very satisfied user.
Jot+ Notes is a free-form note application: No “fields”, no fixed structure. You can organize your data in whatever way suits you! Even better, you can quickly re-organize your data with drag-and-drop ease or let Jot+ Notes help with automatic sorting options.
Fiction writers can use Jot+ Notes to outline the plot, record detailed character biographies, store research materials and notes, and even write the novel/story itself! Non-fiction writers can use Jot+ Notes to maintain bibliographies, citations and references, and more.
Jot+ Notes is also a perfect brainstorming application – put random ideas into individual notes to be expanded upon or deleted as needed.
Other useful features for writers include built-in word count and plugins for spell-checking and a thesaurus.