add a spell checker
On OS X, we'd use the built-in spell checker. For Windows, we're looking at several options, and are currently leaning towards hunspell, an open-source project with support for several languages. The Open Office project also uses hunspell.
I would want spell check to NOT be an automatic thing (like the red underlines in Word, etc). Part of what makes Inqscribe great, and has made transcription nicer, is not being reminded that I make a lot of typos!)