Tiny Spell. Free universal spell checker that will work with any Windows application, monitors from the system tray. Unfortunately no Brit dictionary as yet.
It is a small utility that allows you to easily and quickly check the spelling of words in any Windows application. tinySpell monitors your typing on the fly and alerts you whenever it detects a misspelled word. It also checks the spelling of every word you copy to the clipboard. tinySpell installs itself in the system tray for easy access. It comes with an American-English dictionary containing more than 110,000 words.